I love this idea! Giving simmers this option would mean that people who want to avoid certain situations, whether for the sake of realistic gameplay or for the sake of avoiding bad memories/loss of control, would have the ability to do so easily. In turn, it would mean the dev team could make some more "dangerous" or adverse elements (like not toning down the vampire break-ins so much) in the game for those of us who want them, since they wouldn't have to worry as much about people getting upset. I think two (or three) traits per neighborhood would be plenty, and if someone wants even more, I guess it could be left up to modders.