It never made any sense to me, that the good guy is always murdering everything in his path, or that the stealthy sneak needs to bloody his hands to get a job done. If you want to do a nonlethal run, you need to use melee or not attack whatsoever, making the whole concept really, really strange. Why is that the case when you could simply use a rarer type of ammunition specifically suited towards...
Stunning and Subduing rather than killing
Rewarding the player with good karma for knocking out opponents that would otherwise be killed
Stealthily preventing enemies from detecting your presence without spilling blood
Think about it, it could probably be done fairly easily, and distribution throughout the levelled lists could be done the same as its done in CaliberX, it could be fed through smaller caliber weapons that you could mount a suppressor on, and there could be a few different strengths or types, like delayed delivery, or some sort of debuffing/enraging poison that makes people wig out and attack their allies.
Generally speaking, they're subsonic rounds that deliver tiny little bits of poison, we could go full-on Metal Gear Solid with this s***, and make it so that crits on headshot are garunteed, and that otherwise they have a buildup or something.
Don't make them craftable unless we're talking higher caliber, as .22/9mm/.45/5.56 would all require the pre-war gadgetry that is lost in this age, but add them to some sort of rare levelled list and vendor setting, it'd make the 22 LR pistol usable, and suppressed stealth would make TONS more sense