What I'd like to see in Arma III:
Remove the get up key, make it so Z is prone, and z is to get up. Make it so C and ctrl make you crouch, and when crouched, c and ctrl make you stand up again.
Make grenade throwing less clunky
Add an in-game tutorial for new players, showing basic help on the top left(WSAD to move, left-click to shoot) aka BF2 and Red Orchestra style. It'd react to what the player was doing currently. Such as, if a person right clicks to look through the scope, the basic help would pop up on the top left part of the screen once telling the player how to zone their weapon.
Make entry animations into vehicles longer(OFP style)
Allow players to move(walking) while switching weapons
If Friendly TAG is on, whenever a character makes a radio statement, flash their marker in game.
Disable the binoculars from blocking the view, make it so players are in the unarmed animation when not looking through the binos.