Really do think that soccer-style promotion-relegation would be the thing for football.
I'll throw this out for fun while I'm eating my lunch.
The Premier League is the top 12 teams in the country. I'll use end of 2022 ESPN rankings. So that would be: Georgia, TCU, Michigan, Ohio St., Bama, Tennessee, Penn St., Washington, Tulane, Florida St., Utah, LSU.
That would be a 12-team league, everyone plays everyone once. Top 4 in W-L advance to playoffs. 1 hosts 4, 2 hosts 3, winners meet for the crown.
Bottom 3 get relegated.
There is a Tier II East, Central, and West. That's teams 13-48, roughly speaking, geographically divided into leagues of 12. Everyone plays everyone once, top two teams meet for a promotion game, each of East, Central West promotes the winner of their promotion game to the Premier League. Each receives the most geographically convenient demoted school from the PL. Bottom two teams get relegated from each of the three Tier II leagues, for a total of six going down.
You then have six leagues in Tier III, geographically distributed. This gets you teams 49-120 in the country, which is almost all of current FBS (133 schools). Again, 12 team leagues. Each promotes the winner of its championship game to one of the Tier II leagues, and receives one of the demoted teams from Tier II, again based on geography. Each also demotes the worst two teams to Tier IV.
Then you get into Tier IV, etc.
I have thought that this has been going on de facto for years. Schools with success from smaller conferences like Boise, TCU, etc., even if they don't move conferences, they get "promoted" by getting better TV dates and games. The "group of schools that gets the best TV slots" is really the top tier of college football, which is mostly congruent with (but not always) the top conferences.