I want to see... Ambient occlusion (don't hate me)!
Well you can bake them with vehicles/weapons/bricks/etc with textures so this one is possible
Hard to do, will need to be re-done constantly, but possible
But real-time AO will be cool to have
I'll probably say .DAE support, or anything that wouldn't require outdated software to be exported and won't be buggy and picky
Also improved physics, improved net code, optimization of graphics and maybe their improvement (Better lightning, soft shadows without mods, anti-aliasing without the need to force them with drivers, etc)