I think it will be interesting to see what the Big 12 does. As
@TechRaiderRider just stated, Colorado is probably trying to get ahead of the game. If UO and UW do leave the conference, the Big 12 will have their choice of everyone left. If I were the Big 12, I don't think Colorado would be #1 on my list.
Of the corner 4, my preference would be:
1) Utah
2) ASU
3) Colorado
4) Arizona
That said, I don't know if the Big 12 has the votes to add all 4 of them. I'd imagine some of eastern teams in the Big 12 wouldn't support adding all 4. And you may not be able to separate ASU and Zona.