Playing in a P5 conference will be a lot of fun for Cougar fans (it has been for Ute fans). There will definitely be growing pains as the margin of error will narrow, but you’ll see the football team getting better bowls even in “down” years and playing in new and more historic places. Recruiting will improve and BYU will be in contention for players and transfers they’d previously not. It also helps that the team has been winning recently.
With the eventual loss of Texas and Oklahoma there won’t really be any historic blue bloods in the conference. So it may be easier for BYU to win.
In a side note, I heard an interview with Dave Bartoo (editor for college football matrix) on Kall 700 yesterday. He grades (and consults) coaching staffs among other things (recruiting, team rankings, etc.). He believes that BYUs current football staff (top to bottom) is the second best in the west and would be top tier in the current Big XII. Not too shabby.