But BYU has don't it twice in the regular season - which is what counts here. They have gone 12-0 (or 11-0 in those seasons with 11 games) 5 times 79 and 84 were undefeated seasons and three other times they won 12 straight in a season after an early/first game loss.

I was just saying 3 undefeated P5 teams as an example but it doesn't matter. The same holds true of there are three 1 loss teams and the rest are 2-3 loss teams or any combination you can think of. The point is, the three best P5 teams are irrelevant to the scenario. They are going to the playoff anyway. All BYU needs to be is better than the 4th place P5 team. That is hardly unrealistic.