STANDARD DISCLAIMER: I am NOT saying "ZoS do this now or I'm unsubbbing!" nor am I saying, "ZoS do this BEFORE fixing important issues XYZ!" IF ZoS were to implement any of this it would obviously be up to ZoS to determine how and when. A slow roll out over time would probably be best in fact. So all posts along the lines of "NOOO! ZoS has to deal with "XYZ" that is more important first!" will be ignored. I hope the rest of you with meaningful contributions will simply ignore those (sadly inevitable) posts as well. Thank you. Now, onward...
We talk about end game being where it's at and of course I want to see more end game content because of course I want to keep playing this game AND experience new content regularly. But why is it all about groups, grinding and dungeons? Where are the end game QUESTS? Yes, I know there are some of course but I'd really like to see some game-changing end game questlines that are fun, complex, and really thought out. So I have an idea.
Right now everyone experiences the same quests regardless of their class. What I'd REALLY like to see are end game questlines that are specific to your class. And the end result of such quests would be access to a completely new skill line, rather like the current guild questlines. I'm not going to play armchair dev here and outline what these skills would be or how they'd balance, that's what our clever devs get paid for. So all I'm going to do is talk about what I'd like to see as a player and invite other players to join in and let the dev team know what sort of things you'd enjoy.
And since I feel that vampires and werewolves are (or should be!) their own class, I'm going to include them in this additional end game questline idea and I'll cover that quickly before moving on to my idea for the existing classes.
Vampires: In Skyrim, you can contract vampirism but meeting a vampire lord means you can THEN be "transformed" into his particular strain... almost as if the initial strain you contract merely sets the stage for what you can ultimately become. Vampirism is not completely static in Skyrim. So I can totally see Vet level quests that, depending upon your choices, would set you up to serve one of a handful of different, very powerful, vampires and successfully completing their missions would then result in them "blessing" you with their particular, stronger (edit to add: when I say "stronger" all I actually mean is "more choices" not abilities that are OP), strain of vampirism. It wouldn't really be stronger in terms of game mechanics but would give you new additions to your already existing vampire skill line that you could then choose to replace other abilities with. A "vampire lord" Ultimate akin to Skyrim would be pretty sweet though!
Werewolves: An endgame questline with variable outcomes for werewolves could also be implemented. Perhaps rather than Hircine it could involve the Wyresses, who we already know are shapeshifters. Since being a werewolf IS a sort of shapeshifting perhaps a powerful Wyress can use its inherent magicka to alter and expand it. She sends you on various missions, the end quest reward/result being that she gives you a "pure" wolf form (as in you now have the option to become an actual full wolf), a bear form, or even one of the great cats. Keeping it limited to 3 or 4 large predator animals seems "realistic" from both a lore and mechanics standpoint. I'd also really like to see a questline, perhaps this one involving Hircine instead of the Wyress, wherein you keep the original werewolf form, but gain a new color (your choice of black or white would be SUPER nice!) and new skills. A "call the pack" howl Ultimate would be pretty amazing... you howl and a pack of 3 or 4 wolves appear and fight for you!
I would REALLY like to see these end game questlines open up the possibility of "going to the Dark Side" for characters. Some players just LIKE to play bad guys! And since this happens at end game doing so does not conflict with the original main story questline wherein we are all heroes. Maybe some of us just got tired of maintaining the illusion that everything is rainbows and kittens when in reality we're continually covered in blood.

Thus, these questlines should have very dramatic and opposing outcomes based upon player choices. While there are nearly numberless amounts of "gods" across the face of Nirn The Eight are pretty much universal and so let's go with a storyline where our character is confronted by one of them based on their class and is given a quest of, of course, amazing importance. While on the quest, they are confronted by the Daedric opposite of the god in question and given the option to subvert the quest and serve the Daedric Prince instead. I have deliberately chosen Divines and Daedric Princes we have not yet seen much of in ESO and who would be natural adversaries.
As you can see, this would set up near limitless end game play because there would be so many different possibilities you could go with. You could fill all 8 character slots and still never experience it ALL.
As to the questlines themselves, I am leaving that open because I really want to see player contributions to this. What do YOU think would be awesome as far as both story arc for the quests themselves and new dark/light skill lines and rewards? I personally honestly think we have plenty of epic weapons and armor so would kind of like to see the actual quest rewards be extremely cool vanity items of some sort. So would LOVE to hear ideas for those as well.
So here are the Divines and Daedra I am thinking would be ideal for questlines for each specific class and we can nail down ideas for specifics from there. Please also add ideas for the vampires and werewolves questlines/skills/rewards.
Sorcerer: Julianos (God of Wisdom and Logic )/ Hermaeus Mora (The formless Daedra of knowledge and memory, seeks to possess all that is knowable.)
Dragon Knight: Stendarr (God of Mercy and Justice )/ Boethiah (Deity of deceit, secrecy, conspiracy, treason, and unlawful overthrow of authority.)
Night Blade: Arkay (God of Life & Death )/Nocturnal (Deity of the night and darkness, the patron of all things secretive.)
Templar: Dibella (Goddess of Beauty and Love )/Sanguine (Prince of hedonism, debauchery, and the further indulgences of one's darker nature.)
Okay ZoS community, have at it!
Editing to add: So, say ZoS actually does this. What would you like to see as a questline for Vet characters according to class? What kind of story arch would inspire or intrigue you? What kind of rewards would be exciting to you?