As I understand it BYU would have to be a top 7-8 team but fail to win the conference championship. They’d have to beat out the likes of Georgia, Penn State, Oregon, etc as the 2nd and 3rd place SEC and Big 10 teams.
Maybe the loser of a 12-0 BYU vs 12-0 Iowa State or 11-1 Kansas St game might host but I’d be surprised.