I'm not sure about battlefield, but I would like to see a shooter with massive amounts of (realistic) customization.
First I want all the guns to mimic their real life counter-part: Weight, RoF, Ammunition, ballistics, trajectory, energy, mobility, damage based on where the bullet actually hits etc...
Different styles of all the different possible optics.
All the possible rail systems for that weapon.
Grips, stocks, slings.
All the possible gunsmithing options: trigger jobs, internals, chromed barrels, porting etc...
All the magazine options for that weapon. If I use dual mags I want to pick the style and color of the tape!
Ammunition/barrel changes.
Muzzle options.
Bipods/mounts options that actually work.
Left handed models/mods for lefties.
I want purely cosmetic mods like skeletonized triggers, hammers etc...
Customizable camo that can be tuned to the level.
And 10,000 more options for your actual character.
Then maybe I'd be happy....