Hardcore mode that involves survival aspects such as hunger, thirst, rest, spoiling food, weather adversity, no quick travel etc.
Co-Op. I know purists would ***** about this, but seriously, the game would be that much more amazing with 2 player Co-Op along with scaled difficulty.
Speaking of difficulty: Harder difficulty. Yes mods can fix this, but of all the things to use mods for, this can cause the most problems and it can often conflict with other mods. And make sure it's not just more hit spongey enemies. Make them smarter and more numerous.
More weapons. While the modding community tends to fill out this gap, there's seemingly always a metric shit ton of different swords, but not much else. Would love to see some physics based weapons such as flails or Nunchuku. More maces, spears, throwing weapons, good selection of punch daggers and claws, different classes of crossbow (both light and heavy), various types of short and long bows etc. Just want them to go nuts.
More recognition from the AI relative to who your character is, what they're known for etc. If there's rumours about you murdering people and you walk into a store, I want to hear and see the fear in their dealings with you.
More voice actors: I don't even care if they're amazing. More variety is needed. Heck, have a meet and greet with prospective voice actors from the gaming community. I'm sure you could find a bunch of half decent people willing to work for free just to be in an elder scrolls game.
More meaningful quest choices with consequences. Multiple endings to the main quest.
More factions to join with more side quests.
A larger pool of dynamic, randomly occurring side quests and characters.
More kill animations.
Mounted enemies.