Well, you can ban people from your map, especially when your the map maker. If they're banned from that map, you can just report them for coming into a private map and refusing to leave, can't you? Ad you can just announce to your members who's a mod and who's not. ^^ it would take some coding thoug if it was to become an update, there could also be bugs. Like someone mentioned above, they could be stuck as an actual mod!
I like your idea, though.