Probably the same thing that happens when a G5 makes a NY6 bowl. Sometimes they
win. Sometimes they lose. Sometimes it's a blowout. Sometimes it's not.
The 12 team playoff is essentially the same thing as the current NY6 bowl format. It's still taking the "top 12" teams supposedly. There's still the exceptions for the crappy 3 loss P5 conference champion who is ranked #24 to get in ahead of the one-loss 11th ranked G5 team whose only loss came in their CCG game.