BYU, Cincy, UCF, and MEMPHIS
Memphis is a GREAT college football town - owned by the SEC right now. It's also closer to much of the current Big 12 - and much of the expanded Big 12 than Houston...
The Big 12 has substantial alumni and fans in Houston. They can stage a couple of annual neutral site OOC games and a bowl game in Houston and land the same affect without having to share the recruits and prestige bump with a new Texas institution.