If the Big 12 split, which wouldn't be for at least 8-10 years and who knows what the college football (or ncaa in general) landscape would look like then anyway, then the other 4 Power Conferences would certainly go to 16 each. They would do that now if it was beneficial for them but level of programs, geography, etc. make it so they don't want to do that. If the Big 12 split, there would be ample teams to pick up for those other power conferences wanting to fill the voids and keep up with each other..
The PAC 12 and Big 10 would absolutely wants Oklahoma and Texas, and the Pac 12 would also want Ok State and likely TCU. The SEC would want teams like Baylor and Kansas. The Big 10 would probably end up with Texas in all honestly, and probably Iowa State. ACC would take WVU, hope for Notre Dame's commitment (unless the Big 10 poaches them) . There are currently 64 teams in the P5. If you honestly think that the remaining 4 would go after an alternative to WVU, then those conferences would be trying to sign those alternatives today, which they aren't. It's such an old argument, and holds no water. It's like a SamC argument, just a long diatribe that never has any merit.