Any breakaway is going to include more than just the top brands. Sure, those schools have a lot of fans, but Joe Blow from West Lafayette, Indiana doesn’t care about Michigan vs Ohio State if Purdue is down an entire NCAA division from them.
I think the breakaway is the P5. Maybe a few P5s decide they can’t/don’t want to make the commitment and a few G5 teams decide they can.
I feel like there are already about four levels of FBS. There’s the Big Ten and SEC going forward, then the Big 12 and ACC, then the American and Pac-12/MWC thing, then the Sun Belt, MAC, and CUSA.