The obvious 4 would be Arizona schools, UO and UW.
Utah has been great on the football field, but they do not have a very big brand outside of Utah, they don't contribute a new tv market, they have apathetic fans when their team is down (see the curtains in the Huntsman Center), etc.
Simply put, they don't raise the media rights package, so they are at best neutral revenue for the conference, not revenue adding.
They are far from a sure thing.
The Big12's goal is to solidify themselves as the 3rd best conference for conference security. If you can do that with UA, ASU, UO, UW, then that's the way to go.