Although this idea could be a considerable hit to FPS for some people. But I feel like- through every server, they feel much more lively should you just add NPCs. I do understand there's a certain atmosphere that could be possibly ruined if you were to add locals, but, this adds much more of a lively feel- should you be outside of a night club and there's pedestrians actively going by, and a few select individuals (players) coming into the club itself.
That could kill two birds with one stone. But then that means there'd have to be rules regarding stealing locals cars and the such, or the murder of NPCs, so on so forth.