My playoff scenario is based off bowl game agreements.
The Rose Bowl : Pac-12 Champion vs Big Ten Champion
The Sugar Bowl : Big 12 Champion vs SEC Champion
The Orange Bowl : ACC Champion vs AAC Champion
The Fiesta Bowl : Either MWC Champion vs at-large bid or at-large vs at-large.
The Cotton Bowl : Semi Finals location
The Peach Bowl : Semi Finals location
National Championship game : Cities place bids to host title game.
The four bowl games are played and based on the results of those games rankings are made to rank the teams 1-4. Also Notre Dame does not get special treatment in this scenario. They either join a conference or hope for the at large bid in the Fiesta Bowl.