There was discussion about Old Dominion being unhappy about Conference USA and that they wanted to be the American Athletic Conference's 12th member. I highly doubt they would be first on their list. So who would be? Who will they add (if anyone at all)? Will it be a football only member or an all sports member?
If it were based on football, Boise State is the obvious dream add. I'm sure the AAC will sign BSU up for football only but I'm not sold on all sports. If I'm Temple, I sure wouldn't want to go to Boise in any other sports, especially in the winter. At least all those long trips to Florida and Texas are to warm weather cities. If Boise State takes a football only membership, they would need a home for all their other sports. They used to be in the Big Sky and WAC although for men's basketball both are huge steps down. The WCC would be an appropriate level for Boise State and Boise isn't too far away from Gonzaga. The WCC has no public universities but the Big East (current version) had no public universities before they added Connecticut. If I'm Boise State and I could do AAC football/WCC men's basketball, I would. I remember hearing there is friction between BSU and the MWC.
BYU could be another option. They are happy in the WCC and they certainly would only need a home for football. It would be a good fit for them in the West Division and Navy in the East.
How about Army? Navy's in the conference and Air Force is in the MWC. Why is Army still an independent? It would make sense for Army and Navy to be conference mates. If Army joined, Army would take UConn's place in the East Division and Navy would be stuck in the West Division. Technically the Army/Navy game could be preserved in its usual December date and be considered a "non conference game" every season to not disrupt the AAC schedule and AAC Championship Game. Both teams would play three other cross divisional games and each other, they would make it so they would never be scheduled vs. each other in the "regular season". Technically they could meet in the AAC Championship Game and play twice in two weeks (or just make the Army-Navy game the AAC Championship instead). Army could then have access to better bowl games than they do now.
If academics were any factor, Rice would be considered. They are geographically friendly and a former SWC member with Houston and SMU putting all SWC members in either the SEC, Big 12, or AAC and it would help with travel. The question is would Houston want their neighbors in the same conference again (and would SMU want another Texas team)? Rice was second in C-USA's revenue list (
https://csnbbs.com/thread-896994.html) for 2018-19. Obviously Rice's athletics aren't good.
North Texas would also give the AAC another Texas area school in the Dallas Metroplex although they don't have the SWC history. They're better athletically than Rice but not great. Unlike Rice, a small private school, UNT has a large student body. If the AAC wants to expand in Texas but not duplicate Dallas or Houston, then UTEP or UTSA become options.
In Florida, Florida International has a huge student body, is in the one part of Florida that the AAC isn't (Miami area) and they did knock off the University of Miami in football last year. But their neighbors Florida Atlantic won C-USA two of the last three seasons.
Here's a wild card for you not from Conference USA but from the Sun Belt: Georgia State. It's a market that the AAC doesn't have (Atlanta), a state they don't have (Georgia), a huge student body, and they've won the last two men's basketball Sun Belt championships. As a Temple fan, I'd prefer Georgia State or an Eastern team over another Western team (if you haven't figured out from my posts (Eastern is anything East of the Mississippi and vice versa). They are one of only two R1 universities in the Sun Belt (UT-Arlington is the other and they don't play football).
Another market/state the AAC doesn't have is UAB. Then again, they shut down their football team before reinstating them. Does the AAC want that? Charlotte would probably be a market worth having but of course the AAC has North Carolina already. The best team in football in the Sun Belt recently is probably Appalachian State but they're too close to East Carolina and their market/state doesn't justify two teams.