playoff at all, Boise would be in and BYU would be competing with other non-conference champs for the at-large spots. So it wouldn’t matter if BYU was ranked ahead of Boise St (or the SEC, B1G, or ACC champs).
Put it this way: BYU would just need to be in the top 7 teams, not counting the 5 highest ranked conference champs (which would include Boise in this scenario).