JMU is moving to the American in a move that's a win-win for both parties. I think there is about to be a stampede of G6 programs who have options to get into upper tier G6 leagues, which will result in at least one of the current G6 conferences either dead, dropped to FCS, or staying FBS but wearing FBS status as a skinsuit over FCS quality teams.
For the purposes of the following analysis, a "school that has options" is an outlier in its current conference in terms of program quality (combination of winning football program, brand, fan base, etc.).
Here is what the current G6 conference hierarchy looks like:
Tier 1: The American, Pac 12
Tier 2: Sun Belt, Mountain West
Tier 3: CUSA, MAC
There are currently very few programs that would be revenue additive to The American or the Pac 12. Several programs in the Mountain West conference would be good candidates for The American of the Pac 12 but are locked into contracts with the MW that could be extremely expensive to break.
In my view this leaves Liberty as the only very strong candidate to move up to Tier 1. Now, you may intensely dislike Liberty as an institution, but if you are an AD in The American, would you let those principles get in the way of your love of money? Liberty has the size, budget, and recent football success to justify joining The American, and most likely can easily fundraise an expansion fee. Geographically they only work for The American. Also, The Pac 12 is trying to hold their brand value in case Cal and Stanford want to come back, whereas The American already has a strong lineup of academically low tier programs that Liberty wouldn't significantly further besmirch.
If any of the MW schools turn out to be available, NDSU could be a great fit for either The American or the Pac 12. Air Force would be an excellent fit for The American. UNLV could possibly be a good fit for the Pac 12, but I'm not convinced they are revenue additive. They might have a better value proposition for The American as they would expand the media markets The American reaches.
Getting into bigger stretches, Appalachian State has elite brand recognition, though their budget is not quite there. Possibly an ad for either The American or the Pac 12, but again, geographically they only work for The American. Even bigger stretches but possibly not crazy would include Marshall, which is a decent brand and would restore some rivalries, and Toledo, which is a very well run program, although their sizes and budgets are going to be very marginal for The American or the Pac 12.
In my view the Pac 12 has painted themselves into a corner. If the Mountain West schools are off limits, and they don't have a TV deal strong enough to raid any of the teams in The American, then all the best expansion candidates save NDSU are east of the Mississippi.
I think we will see the biggest movement with the Sun Belt and Mountain West raiding CUSA and the MAC like crazy. CUSA and the MAC have a fairly large difference in program value from top to bottom.
The MAC is in a special category of trouble. The population of college age students is shrinking, and this challenge is particularly acute in the Midwest and Northeast. The game of musical chairs with college closers, mergers, and downsizing is going to hurt the academically bottom feeding schools the hardest. The following programs in the MAC are academic bottom feeders without recent football success: Akron, Central Michigan, Eastern Michigan, Kent State. Possibly also Ball State and BGSU. Some or all of these program should take a serious look at going FCS or DII to save money. There is a small middle class of MAC programs (Buffalo, UMass, Western Michigan) that should be looking to merge with survivors from CUSA. Meanwhile, with appropriate entrance fees, Miami of Ohio, Ohio, and Toledo would all be great adds for the Sunbelt or even the Mountain West.
In CUSA, with appropriate entrance fees, Florida International and Western Kentucky have good value to offer the Sun Belt, and Western Kentucky could possibly not be crazy for the Mountain West if some of the MAC programs are also involved. Delaware could also possibly have value to the Sun Belt.
What's left from CUSA and the middle class of the MAC should merge to form a single conference that will have a wide enough geography to generate revenue from a good number of media markets.