Here's how I view a 12 team playoff - it virtually guarantees that teams like Alabama, Clemson, Ohio State, etc will be in the playoff every year - go back an look at the last time any of these schools finished outside the top 12 in the rankings.
It also should allow for other teams to rotate through and have a chance in the playoff. The big question is: can any of those teams beat the Alabama, Clemson, Ohio States of the world. If not the proposal won't solve the competition problem that CFB has.