My 5 cents:
- new deployable/constructable items = wooden/brick walls and structures, movable ladders/platforms to bypass trenches
- bridges over some buildings
- buildings you can enter
- ghillie suits
- more bushes/items for hiding (Metal Gear's "It's a box!") so AI won't really notice you even if near and other players won't see the circle on your feet
- editable charachters (maybe some colours for pants or weapons)
- editable RPG skills (1st weapon accuracy; 2nd weapon skill; speed; health; leadership; driving ...); once you reach the top skill you begin from 0. More for a rpgish server PvP, PvPvE, Coop...
- customisation of your squad (soldier 1: 1st weapon X; 2nd weapon Y...)
- ingame level editor
- static machineguns overheat or need reloading
- your charachter in the map will be a Star for instance
- linear misions
- more than 1 vehicles performing the same action for AI (3 enemy trasport trucks going together to the same place e.g.; 2 tanks invading together and cooperatively) at the beginning of the steam trailer it appears something like that and looks sweet
- side missions comissioned by hidgher rank AI for you to gain some promotions or RP
- light objects to be thrown (depending on how long you hold a key and the direction you're aiming rather than the position of the cursor)
- missions on pitch black levels or almost complete darkness
I know most of these are barely possible to make, just saying.