Sharing weapons, grenade, and/or ammo.

I think a barebones inventory system would really allow for more emphasis on the teamwork and tactical-side of gameplay. What I mean by barebones, is something like maybe in CS:GO, where you can drop your guns and/or grenades so that other players can pick them up. It'd also be cool if you could pick up your dropped mags from the floor, and maybe have a viable way to drop magazines on the floor for friends with the same gun to pick up.

A good example of philosphy of design: Mid game, you feel you have a good angle on a doorway and want to toss in a flash or a grenade, but don't have one. You can ask a friend to quickly drop a grenade near you where you can pick it up without moving from the spot or fumbling with eachother, and then throw it into the doorway.

It's also be nice to help a brother out when he runs out of mags on his mk18 and you have some spare m4 mags.

I remember this being a pet peeve of mine in Insurgency Source, because the source engine literally has a dedicated feature to drop weapons, but it wasn't in the game officially(at least to my knowledge lol).

I imagine the main problem with this is being able to clone grenades / rockets / guns by dropping weapons and then resupplying at an ammo crate, which could invalidate the entire point system for loadouts.

Giving ammo though sounds like a nice idea. Like if someone is holding an empty weapon and you use the same mags, you can see a prompt to "Hit F to share ammo." I've also been a big fan of the idea of giving rocket/machine gun ammo bags as a backpack option to riflemen, which you could carry to support heavy weapons.