My personal wishes:
Gras:
in Arma 2, the AI doesn't really recognize gras.
My Solution: So... fix the AI or don't implement high gras like in Arma 2. Or both.
Trees:
Arma2: The AI doesn't recognize fallen trees and can see through them but the player can't see through them.
So my wish is don't let the AI see through fallen/dead trees. I
vehicle & tanks vs. trees and fences:
Arma2: Many vehicle vs object collisions aren't very comprehensible.
Like a m1a1 driving over a treetype 1 which has a small trunk and get's stopped but if it drives over a group of treetype 2 which has a bigger trunk it doesn't even get slowed down. And there is a treetype 3 which has a trunk like type 2 but has the same effect like type 1. :P
So my whish is ... make vehicle vs object collisions more comprehensible.
View inside a vehicle
Arma2: Some vehicles like the BTR-90 (i think) have no useable invehicle view, especially the driver's view.
No more of that please. Very disturbing if first person is forced.
Harriers:
Currently i have no clue if you include harriers again but if you do make it possible for the harrier to perform a vertical take-off like it should do.
I think you'll get my points ;)