I don't think BioWare are around the forums much these days, unless they're lurking really hard, but anyway ...
1. I want the if>then Tactics system from DAO and DA2 back, please. The customizable AI was pretty much perfect in DA2, and now it's gone
. The absence of this is the one serious flaw in DAI, as far as I'm concerned.
2. Assuming we're getting a new protagonist, I really, really want race selection back. I coped with human-only protagonist in DA2, but having it back for DAI made me realize how much I missed it while it was gone. And I want to keep all the current races! No cutting dwarves or qunari just because they're not as popular as humans and elves!
3. I want to visit Seheron. I mean, we seem to be going north, and given the map-stabbing it seems that we'll be seeing Tevinter, but I find Seheron in particular fascinating and want to go there and mess around with all the local factions.
4. While the areas could maybe be a bit smaller and we could have slightly fewer of them, I don't want the exploration element removed altogether. DAI is the first BioWare game to include large wilderness areas since the first Baldur's Gate, and I don't want it to go away. They need to refine this aspect of the game rather than getting rid of it.
5. I want better implementation of the tactical camera. Even after patching, it doesn't really get up high enough to allow you to see the whole battlefield in most fights, rendering it useless to me.
6. I want better PC UI and controls (and console UI and controls, I guess, but the PC interface is the one I have to use.)
7. We need more ruthless, mean and downright evil options for the protagonist. I can see why the Inquisitor was restricted by their office (Cassandra, Josie and Cullen wouldn't put up with too much random murderknifing) but I'd very much like to see a return to murder and mayhem for DA4.
8. I missed the ability to be as hilariously inappropriate as Purple!Hawke. ("At least things can't get worse! Today, anyway. I mean, it's pretty late ...")
9. More dwarf lore and dwarf characters.
10. Scout Harding as a companion!
11. Speaking of which: dwarf romance. (BioWare, pls. I have been so patient.)
12. And while I'm on that subject, at least six romances that aren't racegated: two straight, two bi/pan and two gay so everyone has at least two choices. I don't actuall think we need the gated 'extras' like in DAI, although if they want to throw more in that would also be fine.
13. Bring back mounts. Give us even wackier things to ride on. Let us name them. (My nuggalope is Ser Nuggington, Arl of Nugsleigh, but only in my heart.)
... and I could probably keep going all day with stuff I want to see and learn about the world (what is a Fex? Will we ever know?) but that seems like enough to be getting on with.