All signs point to Utah joining the Pac-11. They should not stay at 9 teams because they would be right where they started and Boise would just fill in for Utah. They need to add 3 teams and have a conference championship in Denver.
1st team to add would be Houston. They give you a big market (even if there not important) and a rival for TCU.
2nd team: Fresno State. They are another team that fits the profile of the Mountain West. You want to have quality teams in California and Texas because they are recruiting hotbeds. A rival for Boise State and maybe they could build something with San diego State.
3rd Team: UTEP. There football has just been average but they could be a sleeping giant. The Mountain West gets in West Texas and rivals for New Mexico. Also you would have a TCU-Houston-UTEP rivalry that would cover all of Texas. El Paso is the 6th biggest city in Texas, you can't underestimate that.
4th choice would be Nevada if these didn't pan out.
Splits the conferences like this
East: TCU, Houston, UTEP, New Mexico, Air Force, Colorado State
West: Wyoming, BYU, Boise State, UNLV, Fresno State, San Diego State
Imagine in 2012, a Boise State- TCU championship game in Denver. That would sell out.