Maybe this has been suggested earlier but I haven't exactly read the 200 pages of this thread.
I'd like it if walking on the ground had a little more purpose, from what I know now it's more like an easter egg. But I mean if you managed to get back to a base you should be able to get a new aircraft without having to respawn.
And in multiplayer, they could add like a realism option to this, so that you couldn't respawn unless you died. But the guy walks really slow, so the ability to run would be great.
Also, more vehicles should be drivable, 'cause if you're trying to make your way back to base, what are the odds of finding an unguarded UAZ that you can steal? (Think I saw a simple edit somewhere that made all vehicles drivable, though IMO only the more basic ones should be permitted).
Another thing would be explosions. To me, the mk82 and mk84 explosions look the same size, and both pretty weak in comparison to videos of JDAMs on YouTube.