Assuming undefeated BYU is left out of the CFP. This is because:

1) It's the selection committee's first year. I don't think they rank undefeated BYU behind a 2-loss team in Year 1;

2) The CFP semi-finals host Rose and Sugar Bowls will likely have at least 2 or 3 of the contracted teams in the CFP. So, there will likely be at least 3 or 4 open at large spots for the NY6, which BYU would only need to be ranked at #7 or #8 to get in.

3) The top-15 is jammed right now with 7 SEC teams that play each other. Most will finish with at least 2 losses.

4) The top-25 has a bunch of PAC 12 teams, ACC teams, and Notre Dame that play each other. Most will finish with at least 2 losses.

In the next 3 weeks alone, you have:

#5 Auburn v. #20 Kansas St.
#22 Clemson v. #1 FSU
#18 Missouri v. #14 S. Carolina
#12 UCLA v. #15 ASU
#22 Clemson v. #26 North Carolina
#15 ASU v. #17 USC
#16 Stanford v. #9 Notre Dame
#11 Michigan St. v. #24 Nebraska
#10 Ole Miss v. #3 Alabama
#8 LSU v. #5 Auburn

As BYU keeps winning, the Cougars could easily be in the top 15 by week 7. With 7 weeks left in the season and many more top 10-15 matchups, BYU will continue to rise as it keeps winning. It is very likely that by the end of the regular season and not accounting for conference championship games, at most you will have four Autonomy 5 programs with undefeated records. In that scenario, undefeated BYU is easily in the top-10 and likely inside the top 6-8.