Under the new proposed rules, to make the playoff the AAC champion would have to beat out the 7th place conference champion.

AAC Champions rankings since 2014 (when the CFP started)

2014 - (unranked) Cincy, UCF & Memphis were co-Champs (BYU lost to both UCF & Memphis in OT that year)
2015 - #18 Houston
2016 - #24 Temple
2017 - #12 UCF
2018 - #8 UCF
2019 - #17 Memphis
2020 - #8 Cincy

The top AAC team has averaged a ranking of 14.5 and has made the NY6 (or would have qualified for the playoff) five of the last six years. If BYU can join the AAC, BYU can become the AAC champion on the field by winning their division and then winning the conference title game. This sets the team up with very definable goals for success. Win your division, win the conference title game, make the playoff. As long as BYU can still win their division, everything is still in play.

Highest ranked non-AAC G5 champion

2014 - #20 Boise State
2015 - NA (not top 25) ** the AAC did have 3 ranked teams that year in Houston, Navy & Temple
2016 - #15 W Michigan
2017 - #25 Boise State
2018 - #21 Fresno State
2019 - #19 Boise State
2020 - #12 Coastal Carolina (#22 San Jose St was technically 7th & #25 Oregon was 8th if you don't count #19 Louisiana as a 2nd Sun Belt champ)

The average highest ranked non-AAC G5 champion has finished ranked #20. To win make the playoff BYU would need to win the AAC and then finish higher than the top ranked non-AAC champion or roughly a top 20 finish.

As an independent, BYU would need to finish as the 6th ranked at-large team. The 6th ranked at-large team has been remarkably consistent over the past 7 seasons, only deviating when UCF broke into the top 12 as the 6th place conference champion in 2018.

The 6th at-large team was ranked ...

2014 - #11 Kansas State
2015 - #11 TCU
2016 - #11 Florida State
2017 - #11 Washington
2018 - #12 Penn State
2019 - #11 Utah
2020 - #11 Iowa State

It seems that for BYU (or any team) to earn an at-large berth, they would most likely have to finish in the top 11.

On the other hand, it would seem that if BYU could win the AAC and finish top 20 they would have an above average shot at beating out the 2nd best G5 conference and earning a playoff spot. Finishing in the top 14 would have guaranteed an AAC champion BYU a playoff berth in every year except 2020.

Winning a conference title on the field (no politics involved, just football) and earning a top 15-20 ranking seems like a much easier path than finishing in the top 11.