>Changes/additions to existing lore?
More stuff on the Falmer and Bretons.
>Quests?
Actual choice as we saw in Fallout: New Vegas, for example; multiple ways to actually complete the quest instead of just "do it" or "don't do it."
>Voice acting?
It's continuously improving. Less American VAs, though, more European VAs.
>Gameplay, combat, magic?
Build upon Skyrim, but add more weight to combat, more diverse weapon types, more moves in combat, et cetera (same stuff we've all moaned about before).
>HUD elements, menus?
Again, Skyrim had it nailed down - minimal, clean UI - the only problem in Skyrim's UI was the map which was pretty to look at but not very functional as Morrowind's map was.
>Main story, location, dialogue choices etc…
TES:VI will be in Hammerfell, so I'd like a complex war against the Thalmor which acts almost like an RTS, but in first-person; make it dynamic: what the civil war in Skyrim was intended to be. The main story arc will likely involve swordsinging and Hoonding, so, please Bethesda, make it interesting; make it deep; make it extensive; make it fascinating.