If the next domino here really is two more ACC teams leaving for the Big Ten, and another two leaving for the SEC, then at that point you're down to 8 schools. At that point, if I'm one of the remaining 9, I would be combing through the conference bylaws and the TV contract with ESPN to find a way to make the ACC disappear entirely along with that TV deal.
If they could get rid of Swofford and his lousy ESPN deal and grab a real player to be the commissioner of a new league, I think they might be able to put together a more attractive arrangement for FSU and Clemson than what the Big XII can offer. You'd have Miami, Florida State, Clemson, Georgia Tech, Pitt, Syracuse, BC, Wake, and Duke - some attractive properties and a wide range of pretty large markets in a much tighter geographic area than the Big XII, and without the media market flotsam that the Big XII brings to the table in Iowa State, K State, Texas Tech, etc.
Grab Connecticut to lock down New England's markets, and now maybe you're into a stalemate with the Big XII for a while. Texas and Oklahoma are tremendous football programs, but the depth and media market reach of the new conference would be way stronger.