We usually get DLC that adds new zone or dungeons and some short storyline but the Elder Scrolls series offered some nice random encounters depending on your progress. We all know ebon warrior, some bandit attack, thiefs. There is not quite much of that in ESO. I would love to see more random encounters independent and dependent and on the zone and also storyline and character progress progress.
Random encounters that do not require any progress like bandits attack, thiefs asking for our money or live, small monster attacks and also just random people with interesting dialogues. Each of these scales to your level (more powerfull when you play in group).
Random encounters that depends on the zone, similar to the ones above but with enemy type from the zone.
Random encounters that depends on the progress for example you finish Greymoor so you can be attacked by revengeful vampires, you finished Elsweyr you can be attacked by dragon. Main storyline, more Molag Bal servants attacks.
Group random encounters/events (very rare that offers some nice drops). You are in some city buying some items in the guild store when deadra or dragons, or some other powerfull enemies attacks the City, NPC run away or hide, guards are unable to fight (dead or just unconscious), we can't attack NPC's at the momment but we have to fight a lot of mobs and defeat powerfull boss of even few and we can't just solo such event, wee need other people to help. The event can be scaled depending on the number of players in the city.
I believe this can make the game more alive, worth exploring even when we already now every part of Tamriel. With actually minimum effort every new DLC can add some new random encounters so we can always exceept some surprise. Specific awards like antiques leads, part of rare set, some largere amount of gold, exp buffs.
I would love to see some new approach to the game updates/DLC's. They do not always have to offer new dungeons. Schematism can be boring.