C-USA adding UTSA in 2013; North Texas, FIU, Louisiana Tech also likely - CBSSports
I don't know if you saw this that came out a few days ago, but it appears that FL Int'l, North Texas, La Tech, and UT-San Antonio will all go to C-USA. MWC will add San Jose St and Utah State. With the loss of N Texas and FL Intl to C-USA, Sun Belt will probably add Texas St and N Mexico St as you said. Idaho would be demoted to the Big Sky.
It appears as some have said that this would give C-USA 12 teams and MWC 10 teams, leaving 2 spots open for Boise and San Diego State to come back if the Big East doesn't work...which may appear to be the case.
If the ACC gets split up between the B12, B10, and SEC, then the remnants of the ACC will add most of what would be left of the Big East...BB schools like UConn, Pitt, Syracuse, Cincy, Memphis, etc. The Big East would crumble and Boise and San Diego State would go back to the MWC...But if that doesn't happen then UTEP and UTSA switch to the MWC and the last 2 spots go to Georgia State (Atlanta TV market) and UNC Charlotte in a couple years and the 2 conferences merge in 2-3 years when both their TV deals come up.
It will be interesting to see if anything happens to the ACC this summer though. ESPN would seemingly favor the ACC FB schools to the Big 12. The Big East is planning to hit the open market with their TV rights. But if the ACC is divided up between the B12, B10, and SEC, then the Big East schools join the ACC remnants, then ESPN still controls at least partial TV rights to all major conferences.
And if the Big East did crumble, what happens to Notre Dame? Big 10?