I've thrown around some ideas about the Big East from time to time...
A few KEY points:
1) If the basketball-only schools were to leave or boot the football schools, it should not be anyones assumption that a new conference would be 12 teams. The 8 BE basketball schools might consider reclaiming the Cincy market with Xavier, and might consider another midwest school for Depaul & Marquette by bringing in St. Louis. But an expansion to 12 teams might be a stretch. Why? It's basketball. A 9 team league makes it easier to schedule. It means 18 conference games per year, with each team getting a home-and-home. At 10 teams, it does mean adding a new market and 20 conference games.
I understand that 9 might make the most sense from a scheduling point of view, but the reality is that most bb conferences are between 10-12 members. The only ones left at 9 are the Mountain West, WAC, Big West, and America East. And the first two are non-auto-bid BCS conferences and remnants of what was once briefly a 16-team conference.
I also wouldn't be too concerned about the bb schools leaving under their own volition or kicking the football schools out. I am not even sure they have true solidarity enough to stick together should the fb schools ask between one and four of them to remain in a smaller version of the current hybrid (and this isn't to say it will happen, rather only if on the chance it did happen).
I think the whole situation between the Big East, A-10, and CAA is going to unravel in the next decade changing all three conferences.
As for the football side...
The conference championship game might not be worth diluting the conference. At 8 teams, there is some concern for a defection. But at 9 or 10 teams, there is some ease. Memphis and their basketball program could be enough of a draw to bring them in for all sports. UCF would be gladly included by USF. A long shot 10 years from now could be Charlotte.
I think if there is going to be expansion for the Big East football schools, it is likely to be to 10 teams. I highly doubt UCF would be welcomed by USF, but they just might have to live with it if the other football schools believe it is necessary to have a Florida trip each and every year in terms of football recruiting.
Still having USF as a member has not been as big a boon for Big East schools' Florida recruiting as was having Miami. This may change over time though.