On another blog I wrote about how the Big XII isn't expanding, and how that means it's dying. One of the likely final moves of the Big XII in that scenario involves adding a team from a Group of Five conference. (TL;DR summary: Texas, Oklahoma, and West Virginia have all left, but until then the AAC is still intact.) At this point, the Big XII is about to drop out of Power 5 status, but as it has nine teams, it would be looking to gain another team to at least have an even number and a conference championship game.
At this point, of course, there's no guarantee that the Big XII would be a better conference than the American. But it would have certain a geographic appeal for some American schools, and therefore some of them might jump ship. In that case, the AAC adds someone (likely, in my estimation, Southern Miss) to get back to an even number.
But who do you think leaves?