That would be a good plan, but BYU won't go if they can't have their own channel like Texas.
Nah, they have never wanted their own channel, they want some rights/guarantees to playing some games on their channel, but nothing extreme, not even as much as the Long Horn channel wanted. They want to be able to rebroadcast their games after the fact on BYU.tv, and they would like to be able to broadcast games on BYU.tv that no one else wants to pick up. That's not even real tier 2 or 3 rights, it's mostly just "let us replay games and let us show games that no one else wants". Honestly, I don't think BYU.tv or even no-Sunday play was much (if any) of an issue with previous conference alignment talks. I think the media played/made that up.
This is what I think happened. First, Texas was unsure what to do, whether to join the Pac12 or make their own conf to dominate in a new Big12. I think they did tell the Pac12 they would join with OU, but then either backed out or used it to leverage the rest of the Big12. BYU was a team basically waiting to see where things would end up, and instead of waiting forever, they teamed up with ESPN to get a favorable situation and not be left empty handed, but in doing so, they became entangled in contract promises where they were very beholden to ESPN. Then, the Big 12 needed to expand but I think two things made it hard to pick BYU. First, and most importantly, I think ESPN made talks with the Big12 and BYU really complicated. The TV rights were a problem, but not due to BYU.tv. What BYU.tv wanted was not nearly enough to get in the way of a deal. What ESPN wanted probably was. I think ESPN tried to get too much out of a deal (as they are known for doing), and it was easier and more lucrative for the Big 12 to go with other teams as a consequence. Second, I don't think Texas really wanted to go after more than two teams. I think they might entertain a 12 team conf for a conf champ game, but I think they would prefer to stick with ten teams and only one yearly competitor, Oklahoma. That makes it easy for Texas to get into BCS games and play for MNCs, and keep their program top flight. So once the Big12 got to ten teams, they simply didn't have much reason to keep going and add BYU (assuming ESPN and BYU came down from their early first offer negotiation demands). I also think BYU was still in the honeymoon period with ESPN, and was a little drunk on the new money. They probably didn't think they had to give up too much of their rights deal with ESPN, since ESPN was backing everything so well. Of course in hindsight, seeing conf payouts start going up dramatically to 25million plus, BYU now sees themselves falling behind again. They would probably be willing to accept much lesser terms and join the Big12 now. Timing matters a lot in this whole conf alignment game.
As for BYU and the Pac12, Sunday play was never a real issue, though it was a symptom of the problem. The problem is that BYU is a religuous fundamentalist school, and that is an ABSOLUTE non-starter for many Pac12 schools. The faculty senate of those schools are very powerful, powerful enough to dismiss school presidents and provosts if they are particularly outraged. This was also an issue for Baylor, when they thought Texas and co. was heading for the Pac12, and desperately want to come along. Schools like Cal, Oregon, Washington, Stanford, and UCLA were never going to let BYU join. The money didn't matter. Those schools have faculty who overwhelmingly don't like fundamentalist religions. They can abide a more benign religion, but they are not about to affiliate with Mormons, born again Christians, JWs, 7thDay Adventists, etc. That is the bottom line with the Pac 12 conference, and BYU will never be admitted in the current climate. If BYU wants into a power conference, it's either Big 12, or some kind of Notre Dame-ACC style agreement, probably with the ACC. They will never get into the Big 10 or SEC either.