I've been thinking of this a lot.
I don't think I agree with pks being main char only (I do agree with mugging being main char locked). But PKs are a part of progression in the server as it is required to become made in most factions. Having an alt shouldn't be locked to Associate level.
My alternative suggestion would be to disallow hitmen chars/zips. If the only thing you do is log in to kill someone and do otherwise bare minimum RP. it should be treated in the same fashion as a mugging char, invalidate the rp, and result in punishment. A hitman char is riddled with metagame. Some nigga who you never met suddenly knows what you look like, where you are, and that you're on when barely anyone else is online? Alright.
Doing pks for a faction should require you to be a core part of that factions roleplay, you should have time grinding shipments, running their business, hiring for them. If you are not extensively in the roleplay anymore you should not be allowed to "work" for the family.
Done is the age of niggas who don't even play getting on and thinking they matter.