Yes, this topic has been beaten to death. I stayed away from the subject for some time, but decided to at least leave this outline here describing what I would like to see as a "Vet overland" or a "challenging overland." Please understand that this is simply a perspective that myself and others share, and is intended to be an option. Not forced onto others, not an attempt to hijack the in game market (since that was a point that was brought up before). Just an honest idea from someone who has been with the game for a while and used to enjoy the questing experience, but no longer does.

First are the issues' people like me currently have with overland and questing content.

• Enemies intentionally using abilities that waste their own time or are counterproductive to the fight. This is things like tank npcs leaping out of fights to leave their allies to die, or conjurer mobs summoning literal bubbles that do so little I still don't know their purpose. Many enemy types have abilities like these that take forever to go off and result in nothing if they do, fireworks to make the fight seem more intense without contributing to the fight.
  
• Enemies blending together. Having jumped around several other games lately, and having played games before ESO, it is amazing how little the type of enemy you're fighting matters. An npc dual wielding daggers vs a npc in heavy armor with a sword and shield both fight the same, same hp, same armor, same damage output, with the main factor between the two being which one will pick the 'waste their own time' ability first in a fight.
  
  This makes almost any fight feel exactly the same, and to any player who understands that using an ability that hits multiple targets at once for its full damage, (carve, arrow spray, impulse, exc.) you can kill any group of 3 mobs no matter the composition without even recognizing who you fought. It would make the fights forgettable, but they would have to be remembered first to be forgotten, and they aren't worth that.
  
• Held punches. In the tutorial you are forced to do several things, blocking heavy attacks, bashing to interrupt, cc breaking. Add in something like moving out of red aoe's and these make the core gameplay tools all players have access to. Now, for vet content these skills are used often, more so in pvp, but in overland when do these matter? What mobs aside from world bosses hit hard enough to warrant a block? Which enemies channel spells dangerous enough to be worth your time to interrupt? Which aoe attacks are even big enough for you to find yourself caught in if you actively move during a fight?
  
  Without engaging these core gameplay tools, overland fails to teach players how to use them and fails to engage players who are already used to content that demands this level of interaction. ESO is a fun game to play, but when the standard fights don't even try to ask anything of you in these areas, I could get a similar or better experience elsewhere.
  
• Forgettable bosses. With the One Tamriel update, every zone in the game was brought onto the same level. This is great, since before with zone's being tiered to level ranges if you out-leveled a zone you enjoyed then you had to leave to keep leveling, but not too fast else you enter a zone above your level and hit the artificial difficulty of enemies dodging attacks. The draw back is every zone could be someone's first zone.
  
  But after clearing their first, or second, or third zone, amassing many skills and decent gear, many players would expect the challenges they face to become more difficult to match their expanding skills. Here your only option is to do group content, solo group content, or do solo arena's. Every zone's story is delivered as if to a new player each time, leaving those who already know what kind of path the plot will take with nothing, since the fights don't engage the player beyond 'deal damage and maybe heal some.'

Now, there is nothing wrong with ESO's current overland. The game goes strong because a large enough part of the population enjoys it, and there is a reason why ZOS keeps putting it out as the largest bit of content. But for both long time players who are looking to do something beyond dungeons and trials, and for new players both looking for a challenge, or looking to practice their abilities outside of group content, overland offers nothing. Self gimping doesn't solve the issue of enemies refusing to fight back, it doesn't matter if the enemy type who does that whole 'backup then throw knife' routine takes 10s to kill or 10min, or if his knife one-shots if it lands or just snares. The simple fact is that enemy is a one note challenge that once overcome does nothing to engage a player despite what satisfaction you could gain by waiting next to him for the last second of his throw channel to approach only to interrupt him and leave him in the dirt. The goal of vet overland would be to let the overland content take advantage of all the game has to offer to provide more memorable and meaningful encounters.

Now to get this bit out of the way now, rewards. Many people against this idea point to "you just want better loot" as a counterargument. Some ideas have been thrown around by others with varying degrees of commitment that helped fuel these responses, so here is my offer. Slain enemies award more exp to the same ratio that they do between normal and veteran dungeons (compensating for the longer time to kill them, which isn't even enough as is since people would rather farm normal Blackrose for exp rather than vet), and loot dropped by slain enemies or world events would drop one tier higher (green to blue, blue to purple, purple stays purple), and despite the better quality loot people would still farm normal overland for gear because more chances at a drop are better than fewer unless you only need jewelry.

So, the issues are that fights are forgettable, generally seen as a waste of time and avoided, with enemies who don't stand out from one another and with bosses that leave entire year long stories falling flat for some players with anti-climatic endings. I know this would take time to implement, that time is resources, but if they did this then it could be implemented to every zone both present and future and would help people engage with content they wouldn't otherwise ever think to do. So here are some of the steps to do this.

• Implement an option in some menu to enter "vet overland." On toggle, you would be sent to the nearest wayshrine in a vet instance of your current zone and would be free to turn it off at any time. Note that resource nodes, chest, quest, and the like, all wouldn't award more. Just enemies killed, since they are the only place where difficulty would be altered.
  
• A slight buff to mobs health and damage, enough to make them survive long enough to act and hurt enough to be worth notice.
  
• Remove worthless skills from enemies.
  
  Don't have tanks leave the fight and let their allies die, only to return a few seconds later to be killed off themselves. Instead, let them use guard more, and chains and roots, plus a healthy amount of armor to make people actually understand why armor pen is a thing.
  
  Take the literally worthless conjurer bubble and replace it with any other summon.
  
  Have necromancers raise multiple undead at once then use an aoe buff rather than a single target one. That would make any fight with multiple necromancers more interesting, more so if there are already some undead in the area.
  
  Have npc healers actually heal. Give the standard healers the same aoe heal some elite mobs have, like the ones in White Gold Tower. Let them use the single target heal without cooldown unless interrupted so they don't waste time trying to do pitiful damage.
  
  Let fire mages summon large fields of fire that deal more damage, encouraging players to work around the hazard rather than just being amused with the fire puddle placed on a random crate away from the fight.
  
  Give frost mage shields the same trait that the druid totems in Selene's web have, encouraging ranged mobs to stack behind it for protection. The AI doesn't need to be overhauled, just passive synergy would be enough.
  
• The equally challenging part would be tweaking bosses. Wouldn't be nearly as impressive as what we see in dungeons, where the dev's have plenty of time to script out each fight, but they wouldn't need to. Finding interesting combinations of mobs plus a boss with an ability that plays to those mobs strengths, or finding a set of abilities that synergize in an interesting way, would be enough to at least make these encounters memorable. Like, say, a necromancer boss that endlessly summons mobs, so their necromancer minions can buff them. Or a frost mage boss summoning spikes of ice that also have the 'projectile shield' ability, providing their minions' protection. If mobs would fit a boss that doesn't have any to begin with, then a simple ability that triggers at the beginning of a fight to summon them in would be enough, no need to even modify the world space. Things of that nature.

Like I said, I understand this is a tired subject and many have already made their call on which side they are on. But please understand, it is fine if people enjoy the content as it is, it is fine if people would like to see it improved, this is how I would see the option added for those interested so that they may enjoy more of the game, and I leave it to the forums to do whatever with.