IIRC, one of the sticking points when Texas(and other schools) flirted with the Pac-12 last year was The Longhorn Network.
The big thing to me about the Pac-12 is the lack of overlap in the BCS conferences, they pretty much have everything west of Texas
Yeah, the Pac-12 won't bend on the Longhorn Network (conference owns/sells all TV rights) and UT won't give it up. As long as it exists it will always be a barrier to Texas joining, and there may not be a middle ground on which to compromise.
The Pac-12 is the only BCS conference without an overlap. Of course with the geography and population disbursement out here, there are no other expansion options that make financial sense for the Pac-12 other than Texas. BYU does have some appeal (well-known brand, national following among LDS), but they were long rumored to be a Pac expansion target and the conference insisted it wasn't interested because BYU doesn't fit their profile and the ban on Sunday games created too many scheduling problems for non-revenue sports.