BYU and Utah make the most sense. They are both good academic and well rounded athletic institutions. Additionally, they follow the trend of rivalry pairs (two AZ, two OR, two WA, two so-cal, two nor-cal, and then two UT schools) and are far enough west to make sense.

I’m not sure how you’d effectively split the conference with BYU and Utah added.

North: UW, WSU, Oregon, OSU, Utah, Cal
South: Stanford, USC, UCLA, ASU, UA, BYU

Splitting up Stanford and Cal across divisions would be kinda’ counter-productive, but not sure what else you could do. Still play 9 conference games, with the divisions playing a full-round robin and then a random slate of 3 games from the south division, with allowances made for traditional rivalries (ie, Utah and BYU always play each other, same for Stanford/Cal, etc.)

I’ve always thought adding BYU and Utah was the best bet for expansion. Both are competitive in football (and BYU has a great football history), and both are about on-par with the Arizona schools academically.

Both Boise State and Idaho State are viable options. UNLV and UNR are both rivals, and there’s also the option of Hawaii and Fresno State. These schools have had recent successful seasons, but didn’t earn that much respect from voters because they weren’t in a good conference.