Exiled BBMBers will continue to get sh*t no matter the format of the board.
But srsly, I don't think this feature would be about "dividing" anyone, and I certainly don't think SDS or the mods would let that happen anyway. I'm envisioning it looking kinda like the current setup of sub-forums, but with users having much more say in the creation of those sub-forums. So, like in my example earlier in this thread, I could see a "Rochester Fans" club being useful. We can talk about where in town to go watch the games, best routes to/from Orchard Park from ROC (if you're not in a hurry post-game, 20A all the way to Warsaw and then up 19 is a gorgeous and relaxing drive in the fall), rendezvous points for carpools (my crew always uses the Home Depot parking lot off of 490/Buffalo Rd in Gates) and any other random things only ROC fans would care about, without cluttering up any main boards.
So I see it as being a constructive way to have people gather around shared interests, and not a way to create "Elite Posters Only" clubs.
EDIT: One other point, because I see the other thread on the message board migration has been locked. I would very much be in favor of purging inactive users, selfishly because I'd like to change my screen name to "jimmy." There is a "jimmy" on the roll, but he signed up 13 years ago and hasn't been active since.