The 7 player vanilla games have their own appeal, and I suspect lots of regular players enjoy them just as much as the larger games.
Present the 7 player game as being just as challenging as the larger games. Experienced players might be
more likely
to join if they aren't expected to play as teachers. New players are going to join whatever game they please, and if the "this is the place for stupid players" stigma is removed, I would assume everyone would try a 7 player game first, as they are less demanding.-Peter