That means your playoff should include at least 5 teams...and I don't understand why the conferences decided a playoff with fewer slots than the number of (Power 5) conferences made sense.
The 3 at-large (or wild-card) team selections accounts for ND, other really good teams not conference champions, and someone like UCF getting a shot.
Hell...the FCS does it for 20 teams (10 conf champs plus 10 at-large)...and that seems to work.