I think, that there should be ingame achievments... These achievments then lead to perk unlocks, upgrades, or temporary abilities... These achievments can start over at the end of each round or go on permanently.
Second idea: Traitor perk: The ability to set traps. Eg: tripwire, pressure pad/plate, bear traps... These traps can disorientate, blind, or hurt the player.
Third idea: Detective perk: magnifying glasses. Use: use on bodies to find extra information about cause of death. Eg: player ***** and ****** were closest to this person at death, it took 2bullets to kill this player (incase you check peoples guns), (if just found the body few seconds after incapitation) which direction the player came from.
Fourth idea: innocent: if at a certain amount of Karma the innocent would be Special Innocent. Being able to have extra health, ammo, and to be able to (before death) be on ground with a few seconds left to give being able to shoot with a handgun.
fith idea: traitor: a high tech camo suit, which (for a few seconds) if worn use the primary button to turn invisible without moving, or takes the material you're closest to and disguises as that...