Game is in a weird spot right now where it tries to be realistic but also keeping some arcade game design to keep it fun, so I think this suggestion might get some hate. (I know milsim/hardcore mode is coming, so this suggestion might as well be used in that mode when it launches)
but the premise is simple, can't revive teammates if they have been shot to the head.
any other cause of death can still be revived from (explosions, falling, vehicle collision, shots to any other body part area)
since helmets already give you a second or in some rare cases, a third chance, I find it fair that you will not be given any more chances after that
this is a great solution to dispatch enemy nests or camping spots without having to worry that the person you just killed will be revived back, rewarding good aim
"If you want the game to be more realistic then stepping on a mine or getting killed by a RPG/grenade should be the same"
well, this is true.. can't argue with ya! but I feel like having "headshots" to be the only kind of non-revivable cause of death already being very game changing
"What about people that don't use helmets in their loadouts?"
You should always bring a helmet to the battlefield :)
Another way of doing this is that, Medics are the only ones that can revive you if you have been shot the head, any other role can't, rewarding squads for having at least one medic, and giving this role more purpose (now since everyone has the same bandaging speed and 50 points of health per bandage)
Feel free to discuss if you have any suggestions to improve this idea