There has been talks in the past about possible karma system. In one previous EFTBot video one streamer accidentally found a random piece of text in the lobby that refered to it, proving that BSG is at least thinking internally about it. Nikita has not confirmed nor denied anything, so I suppose it is understandably a longer work in progress.
In my humble opinion, karma system for PMCs wouldn't really make sense. As PMCs we need to be hunted by the environment. We cannot be restricted by a point system, since that would go against our FPS instincts. You can't be looking at a player approaching, wondering if it is a USEC/BEAR and if he is going to play by the rules. That is why I would suggest PMCs not having a Karma system, apart from the current one reflected in traders.
Player Scavs, however, could use a proper karma system. If you execute several AI Scavs, word should spread. Over time, your Scavs clothing and visage could change, perhaps to resemble the old Bandits from STALKER. Your weapon choice could potentially change, along with the random gear/loot you have on you when you spawn. This would give other Player Scavs a visual clue on if they should shoot you on sight or not. If you go psychopath enough, Scavs could start first warning you not to approach them, then after more Scav kills just shooting you on sight.
On the other hand, if you are chill in your raids, don't execute other Scavs (both AI and Players), your karma could turn up positively. I am not sure what getting positive karma would entitle apart from that, that can be figured out. However, your visage could turn more positive again. Your gear could also be affected; since you are playing with little violence, you could have a less combat oriented loadout with more interesting random loot in your pockets. The Scav interaction could also change; if you top out your Karma, Bosses could potentially scream at you and order you to leave their area, instead of just shooting you on sight. Of course, if you got closer, they would still start shooting.
There is many little things that could be attached to the Player Scav Karma system. I suppose that my main idea is that PMCs exist in a shoot on sight world. Player Scavs don't, but this is where we could get some interesting RPG elements to distinguish the Player Scav raids from PMCs.
This is my first post on reddit, so I hope it makes sense. Even if it doesn't, thank you for reading.