U can see where this is heading. Two major super conferences with "4" divisions each. Each division would have 5 to 6 teams. Winner of each division makes the playoffs. My bet is that leads to an "8" team playoff. 1st Round occurs in early December. Semifinals in and around New Years Day with Championship game just like today. Each year it will be the BIG vs SEC for National Championship.
My guess would be the divisions would be location specific except for Notre Dame. If they expand to 24 teams add a few more ACC teams plus another PAC 12 team. Each Division rotates through the other Divisions on a yearly basis.
20 Team: BIG Divisions Example
West Division: Notre Dame, Oregon, Stanford, UCLA, USC
Central Division #1: Iowa, Minnesota, Nebraska, Northwestern, Wisconsin
Central Division #2: Illinois, Indiana, Michigan, MSU, Purdue,
East Division: Maryland, North Carolina, Ohio State, Penn State, Rutgers