Religion has always played a large part in the elder scrolls lore, stories and quests; the daedric princes are quite powerful, active, and sometimes petty; even the less present aedra do occasionally make their touch felt on Nirn - while both and others besides them have a large number of people following them, asking (and sometimes receiving) favor through prayer and sacrifice, worship and devotion, while otherwise advancing the cause of their deity throughout Tamriel.
Players in ESO encounter this often enough, from the mainstory conflict with Molag Bal and his cultists, through more or less close encounters with other daedric princes to meetings with followers of the aedra or other powers, even the (costly) small touch of aedric power for the final fight... would it not be logical to take the next step and allow players to pray at shrines for a divine blessing, curry favor with the priesthood to receive special training, and even align themselves with any of the numbers of powers that can be found in the various pantheons of the elder scrolls?
In that spirit... let’s talk elder scrolls religion!
Temples and Shrines
All the religions in Tamriel have their shrines. For some like the eight divines, these shrines are proudly displayed in a cathedral, found in almost every major city. For others like the daedric princes, those shrines are usually well hidden and their followers meet in secret, lest they be arrested by the guards. And some religions still are somewhere in between the two... more regional religions for example, like the Hist worship in Black Marsh or the Tribunal in Morrowind, which are present in their regions, yet not found anywhere else...
There are many such places in ESO already, from cathedrals and temples in High Rock and Hammerfell, Auridion or Elsweyr... shrines in Skyrim and Valenwood, the tribunal temple in Mournhold and Vivec city, or the shrines near Ebonheart, and so on... even several hidden daedric shrines, from a certain cabin in Stormhaven to a gathering of cultists in Cyrodil... this could easily be expanded, adding one individual shrine to each of the eight divines to those cathedrals, and well as more shrines in several likely locations... the Mournhold temple would make a logical choice for Tribunal worship, as would Vivecs temple in Vvardenfell or clockwork city, there are at least a few argonian ziggurats that would make perfect places for Hist worshippers to mingle, though technically every big hist tree could serve as "shrine" for them also, the Yffre worship in Valenwood also has several locations where a shrine would seem logical, and even the daedric princes can have nice things (or places) like Azuras temple in Stormhaven, an obvious shrine for Malacath in Wrothgar, or Beotiahs influence in the Dragonstar Arena that makes it a likely place... others may be more hidden, like Molag Bal could have a shrine in the cavern in Stonefalls where you may end up disturbing some of his followers depending on your quest choices, or Clavicus Vile has his fingers into at least two towns in the old mainstory regions, each of which has a shrine location that could very well be active for worship after completing the questing there, Namira has some places in Stormhaven, etc.
For player character religions though, shrines are important. For one, declaring oneself to one religion would obviously happen at a shrine, for another, shrines and their accompanying priests would be a good place to receive and turn in daily quests, or receive blessings.
And yes, that means that it would be very easy to follow one of the divines... with cathedrals and places of worship all around Tamriel... but somewhat hard to follow a deadric prince... who may have one secret shrine tucked away in some dark corner of the world, or possibly even hidden in a dwelve... (those are the trials and tribulations of following the gods of oblivion after all)
And of course, a small corner shrine that dispensed blessings upon "prayer" interaction -would- make a perfect addition to the housing system...
Prayer and Blessings
The main benefit of religion anyone can benefit from might be receiving a small temporary blessing from a deity in response to a prayer at their shrine. That blessing would have to be something in theme with your deity, lasting a good deal longer then food buffs – several hours at least, since it needs to be refreshed at a shrine, and have only a minor effect in game... something like taking less damage from undead when protected by Arkays blessing, or restoring a bit more health when healing while empowered by Mara, gaining a bit of boost to destruction magic from Mehunes Dagon, or whatever.
Every character should be able to approach every shrine for a blessing, but the actual effects ought to depend on the characters declared belief and the interaction with the shrine choosen. Meaning a devout follower of Akatosh will receive boosted blessings from Akatosh as his choosen diety, yet receive normal blessings from other divines, but gain a -debuff- instead of a blessing if they were to pray at a deadric shrine, because the aedric and daedric powers are opposed. Thus are the punishments for praying to "strange gods"! Some deities may leave more options then others... a follower of Stendarr for example could gain blessings from all the other seven divines as well, but a follower of Azura might only be able to count on the other "good daedra" while finding the "house of troubles" opposed to them as well... in addition to having less easy access to shrines – again, thus are the trials and tribulations of following "dark gods"...
A character who had not chosen any deity on the other hand could receive blessings from Akatosh today and from Mephala tomorrow, but would only ever receive the standard blessing, never any boosted blessing. And it might even be possible to have a religion without blessings – for example, it would fit the Tribunal not to dispense blessings per se (something supported by the existence of "blessing stones" as an artificial means of bestowing divine power to something or someone), but gain their followers a different advantage (like for example, better deals from all vendors in tribunal territory... and/or worship experience/tokens just for praying...)
Obviously only one blessing could be active at any given time, and any new prayer would replace it with a new blessing where applicable.
Followers and Worship
Many people declare themselves to follow one power above all others. In addition of receiving stronger blessings from their patron deity, they might also gain a small passive skill line to reflect their faiths peculiarities... and their standing within the religious community. Which would more reflect special training and teaching that happens during the course of worship then any divine blessing (since that is a different mechanic and thus should have a much lower game effect). It’s like... if you follow a healer god, it just makes sense that you'd pick up more tricks about healing; if you follow a spider goddess, it may just be that the rituals involve drinking concoctions including some small doses of spider venom, resulting in a little resistance to poison; if you follow a warrior god, it just makes sense that in the course of worship some of the older warriors following that god might mention that neat trick you can do with your shield if the enemy comes at you like -this-... et cetera.
Such a skill line would be advanced by completing faith specific daily quests, and possibly also by daily donations - though not every deity may take gold, some may require the burning of provisioning ingredients, or crafting materials, or even specific actions, like standing over a kill in cyrodil and using an item (undoubtedly kept in a bag with a big "T" written on it) to dedicate it to your deity, being open for attack all the whole - but unlike other skill lines you can also -loose- progress by committing acts of sacrilege, doing things your deity (and fellow followers) would find disagreeable. Obviously you could always make up for it by doing more daily questing or donating to reaffirm your devotion...
Naturally people can also leave a religion, break all ties with their god, and be free to worship some other power, or none at all. After all, that sort of thing happens all the time, today and in history - people leaving their birth religion in disillusionment, converting to a new faith or none at all, joining a cult or suddenly finding religion after a life of atheism... This ought to work pretty much like getting rid of vampirism and werewolf status - and indeed, the "Follower" skill line ought to be mutually exclusive with both vampirism (since you swear off both aedra and daedra in their initiation quest) and lycantropy (since that basically is declaring for Hircine anyhow).
Religious Passives:
• Initiated: Unlocks special faith vendor where faith tokens from daily quests can be exchanged for faith-relevant gear or outfit options
• Devotion I-IV: Gain increased blessing duration.
• Fervor I-IV: Gain additional daily quests for faster advancement
• <Faith specific Trainings>: (will give a small bonus to something relevant to the worship, as well as an bonus to advance one skill line similar to the racial advancement benefits)
• Annointed: chance to gain double effects for blessings
Gods and Pantheons
There are many dieties worshipped in Tamriel, though maybe not as many as it sometimes seems since some are worshipped in different regions under different names. Some may have several shrines in major cities all over Tamriel, some may have shrines only in one specific region, and others still may have a single well hidden place of worship. Obviously finding all the shrines would make a nifty achievement, yes?
The Eight Divines and their Religion:
Akatosh / Auri-El / Ruptgar
• Sphere of Influence: Dragons, Duty, Endurance, Time
• Blessing Effect: Damage/Heal Over Time bonus
• Faith specific Trainings: Damage Over Time resistance & Draconic Power advancement bonus
• Daily Quest: Dutifully spend time completing any other daily quests...
• Sacrilege: Shirk your duty by abandoning a quest, or failing to complete it in a timely manner...
Arkay / Tu’whacca
• Sphere of Influence: Death, Funerals, Life
• Blessing Effect: Reduced damage from undead opponents
• Faith specific Trainings: Bonus damage against undead & Dawns Wrath advancement bonus
• Daily Quest: Lay <×> undead to their delayed final rest.
• Sacrilege: Respawn after being killed, revive others, fill soul gem
Dibella
• Sphere of Influence: Affection, Art, Beauty, Music, Passion
• Blessing Effect: Increased duration for CC effects
• Faith specific Trainings: Vendor buying bonus & Jeweler inspiration gain bonus
• Daily Quest: Do <×> social interactions (play music, dance in taverns, converse with civilians, etc)
• Sacrilege: Destroy artwork, kill artist NPCs, some quest choices
Julianos / Jhunal / Xarxes
• Sphere of Influence: Law, Language, Logic, Magic, Wisdom
• Blessing Effect: Bonus spell resistance
• Faith specific Trainings: Increased magica regeneration & Mages Guild advancement bonus
• Daily Quest: Donate <×> writings (motiv pages/books, recipes, maps, pardons, etc.) to the temple
• Sacrilege: Pay fence to clear bounty, use forged pardon; destroy writings (see above).
Kynareth / Kyne / Khenarthi / Kaan / Tava
• Sphere of Influence: Nature, Wind and Sky, Hunting, Warriors
• Blessing Effect: Bonus resistance to slow/snare/immobilization effects
• Faith specific Trainings: Increased non-combat running speed & Storm Calling advancement bonus
• Daily Quest: Hunt <×> of each meats (red meat, white meat, small game, poultry) for temple
• Sacrilege: Run from a fight (when aggroed mob thethers out)
Mara / Morwha
• Sphere of Influence: Compassion, Fertility, Healing, Love
• Blessing Effect: Bonus healing done
• Faith specific Trainings: Disease damage resistance & Restoring Light advancement bonus
• Daily Quest: Gather <×> healing herbs for the temple
• Sacrilege: Murder Innocent, use Blade of Woe, Ignore streetside beggar, refuse request for aid
Stendarr / Stuhn / HoonDing
• Sphere of Influence: Justice, Charity, Luck, Merciful Forbearance
• Blessing Effect: Bonus critical hit chance
• Faith specific Trainings: ? & Aedric Spear advancement bonus
• Daily Quest: Hunt down <×> bandits; donate gold to temple
• Sacrilege: Murder Innocent, fence stolen goods, pay fence to clear bounty, use forged pardon
Zenithar / Tsuhn / Xon / Z’en / Zeht
• Sphere of Influence: Work, Farming and Commerce
• Blessing Effect: Bonus for selling & buying, increased rewards for crafting writs
• Faith specific Trainings: Vendor selling bonus & Crafting inspiration gain bonus
• Daily Quest: Complete one gear and one consumable crafting writ
• Sacrilege: Steal from lockbox/home, pickpocket NPC (thieves caches are fair game!)
The Deadric Princes and their Cults:
Azura
• Sphere of Influence: Dusk and Dawn, Twilight, Magic, Vanity
• Blessing Effect: Bonus ultimate gain
• Faith specific Trainings: Reduced spell cost & Dark Magic advancement bonus
• Daily Quest: Collect (random) ingredients for priesthood rituals
• Sacrilege: Use any [Lie] dialogue options (Vanity!)
Boethiah / Boetra / Dark Warrior
• Sphere of Influence: Deciet, Conspiracy, Plots, Treason
• Blessing Effect: Increased physical damage
• Faith specific Trainings: Increased spell resistance & Siphoning advancement bonus
• Daily Quest: Defeat enemy of higher alliance rank or <×> enemies of any kind in PvP
• Sacrilege: Increase alliance rank (loyal service!), complete Deshaan mainstory chapter
Clavicus Vile
• Sphere of Influence: Wishes, Bargains, Deception
• Blessing Effect: Bonus to any reward pack or chest content roll (get lucky on your wish!)
• Faith specific Trainings: Vendor Discount (Bargain!) & Daedric Summoning advancement bonus
• Daily Quest: Fulfill a quest, keep your bargain.
• Sacrilege: Abandon quest (break bargain), complete Vvardenfell mainstory chapter
Hermaeus Mora / Herma-Mora
• Sphere of Influence: Forbidden Knowledge, Memory
• Blessing Effect: Increased motiv/recipe/blueprint drop chance
• Faith specific Trainings: Bonus Spell penetration & Mages Guild advancement bonus
• Daily Quest: Read a number of books (aka, check ten different bookcases for example)
• Sacrilege: Destroy any crafting recipe/diagram/motiv, etc.
Hircine
• Sphere of Influence: Hunting, Manbeasts
• Blessing Effect: Werewolf transformation duration bonus
• Faith specific Trainings: None because Werewolf!
• Daily Quest: None, just hunt as Werewolf!
• Sacrilege: Cure werewolf status
Malacath / Trinimac
• Sphere of Influence: Strength, Honor & Vengeance, Oaths & Curses, Outcasts & Unity
• Blessing Effect: Increase physical resistance OR physical damage (random)
• Faith specific Trainings: Increased elemental resistance & Animal Companion advancement bonus
• Daily Quest: Complete any Orsinium daily quest,
• Sacrilege: Complete quests that require slaying more then <×> Orcs, Ogres or Ogrym
Mehunes Dagon
• Sphere of Influence: Destruction, Change, Revolution, Ambition
• Blessing Effect: Destruction staff bonus damage
• Faith specific Trainings: Fire resistance & Destruction advancement bonus
• Daily Quest: Kill <×> enemies with destruction magic only
• Sacrilege: Use restoration magic or any other healing spells
Mephala
• Sphere of Influence: Murder, Sex, Secrets, Spiders
• Blessing Effect: Increased critical chance
• Faith specific Trainings: Increased poison resistance & Assassination advancement bonus
• Daily Quest: Murder any innocent
• Sacrilege: Get spotted murdering (keep it secret!), complete some Summerset quests…
Meridia
• Sphere of Influence: Life Energy, Light, Colors,
• Blessing Effect: Bonus damage against undead opponents
• Faith specific Trainings: Bonus stealth detection chance & Dawns Wrath advancement bonus
• Daily Quest: Kill <×> undead or complete Dolmen
• Sacrilege: Fill soul gem, use soul gem to recharge weapon
Molag Bal
• Sphere of Influence: Brutality and Domination, Soul Enslavement, ***, Necromancy
• Blessing Effect: Increased Soul Lock chance
• Faith specific Trainings: CC duration bonus & Bone Tyrant advancement bonus
• Daily Quest: Fill <×> soul gems
• Sacrilege: Defeat any Dolmen, complete any mainstory chapter or coldharbour quest/dwelve
Namira
• Sphere of Influence: Decay, Spirits, Ancient Darkness, "Creepy Crawlies"
• Blessing Effect: Bonus to damage over time effects (Decay!)
• Faith specific Trainings: DoT resistance & Grave Lord advancement bonus
• Daily Quest: Do <×> DoT damage
• Sacrilege: Purge any DoT, complete Shadowfen Xal Ithix questline
Nocturnal
• Sphere of Influence: Night & Darkness, Thievery
• Blessing Effect: Increased stealth effect during nighttime
• Faith specific Trainings: Reduced stealth cost & Thieves guild advancement bonus
• Daily Quest: Steal and fence <×> loot
• Sacrilege: Let yourself be caught by guards, complete CWC & Summerset mainstory chapter
Peryite
• Sphere of Influence: Tasks, Pestilence, Natural Order
• Blessing Effect: Bonus disease damage
• Faith specific Trainings: Bonus disease resistance & Living Death advancement bonus
• Daily Quest: Inflict <×> disease damage...
• Sacrilege: ...some "cure illness/disease" quest completions
Sanguine
• Sphere of Influence: Debauchery, Revelry, Passion
• Blessing Effect: Bonus to health (to endure all the partying)
• Faith specific Trainings: Increased drink buff effect & Provisioning advancement bonus
• Daily Quest: Use <×> drinks and <×> dance emotes (aka, get drunk and party!)
• Sacrilege: Spend a game-day (6 hours playtime) without food or drink buff active
Sheogorath / Uncle Sheo / Skooma Cat
• Sphere of Influence: Madness!
• Blessing Effect: Random! (It’s like a box of chocolates... you never know what you’ll get!)
• Faith specific Trainings: Chance to ignore fear effect & Daily random skill line advancement bonus
• Daily Quest: Random! But always something pretty whacky and nonsensical...
• Sacrilege: ...nothing is too insane for uncle Sheo!
Vaermina
• Sphere of Influence: Dreams, Nightmares, Evil Omens, Torture
• Blessing Effect: Bonus CC duration
• Faith specific Trainings: Reduced fear duration & Shadow advancement bonus
• Daily Quest: use <×> mental CC effects (stun, fear) or taunts
• Sacrilege: attack "sleeping" NPCs, complete Stormhaven mainstory chapter
Other (local) Powers and their Faith:
The Tribunal Temple (Almalexia, Sothra Sil, Vivec)
• Sphere of Influence: Dunmer
• Blessing Effect: Increased experience gains in dumer lands only
• Faith specific Trainings: Increased quest rewards in dunmer lands only
• Daily Quest: Pray at each of the tribunal members shrines
• Sacrilege: pray to any other power
The Green Pact - Y’ffre / Jephre
• Sphere of Influence: Nature, Plants, Forest, Song
• Blessing Effect: Bonus Health Recovery in Valenwood regions only
• Faith specific Trainings: Stealth bonus (blend in with nature) & Green Balance advancement bonus
• Daily Quest: Hunt <×> prey animals (those that graze on plants, not those that hunt for meat)
• Sacrilege: Cook or eat food made with plants (pretty much most of them), harvest living plants (alchemy, clothing)
The Hist
• Sphere of Influence: Argonians
• Blessing Effect: Increased experience gains in argonian lands only
• Faith specific Trainings: Increased quest rewards in argonian lands only
• Daily Quest: Fertilize a hist tree (with some -fresh- ingredients)
• Sacrilege: fill soul gem from argonians (prevent their spirits return to the hist)
Baan Dar
• Sphere of Influence: Thieves, Beggars, Tricksters, Pariahs, Archery
• Blessing Effect: Increased experience gains in Valenwood and Elsweyr lands only
• Faith specific Increased pickpocket chance & Bow advancement bonus
• Daily Quest: Pickpocket <×> people or find and chat with M’aiq
• Sacrilege: Get caught and have to pay your bounty to a guard
Masser & Secunda / Jone & Jode
• Sphere of Influence: Khajiiti births & culture, mortality
• Blessing Effect: Increased experience gains in Elsweyr regions only
• Faith specific Reduced fall damage & increased quest rewards in Elsweyr regions only
• Daily Quest: Complete any daily quest in Elsweyr regions
• Sacrilege: Respawn, revive others, use necromancy pets (ignore "bounds of mortality")
Magnus
• Sphere of Influence: Light, Sight & Insight, Magic
• Blessing Effect: Bonus to spell damage for mages guild members only
• Faith specific Bonus to Mages Guild effects & Mages Guild advancement bonus
• Daily Quest: Complete one mages guild daily quest
• Sacrilege: Complete PvP quests when your alliance is dominant (upset balance!)
Syrabane
• Sphere of Influence: Magic, Apprentices
• Blessing Effect: Increased reward chance from Psijic Portals
• Faith specific Bonus to Psijic effects & Psijic advancement requirement reduction (1 seal)
• Daily Quest: Complete Summerset Geyser daily or loot <×> Psijic Portals
• Sacrilege: Learn & use Stamina Morphs... (magic apprentice, not warrior!)
(And yes, all those are just some rough ideas to give people a notion of what -could- be, just off the top of my head. There could be more added, some removed, and most changed, its just a concept after all!

)