I say 8 team playoff at the most. ACC, Big Ten, Big 12, PAC 12 and SEC champs get in. Then 3 at large. 1v8, 2v7, 3v6, 4v5.
I don't like the 4 team format. It will be fun and interesting but if it was in place this year, Mizzou would have fallen out and been punished for getting to SEC title...