Athletically SEC is a good fit, but the "academics lobby" at UT prefers the Pac-12 and ACC. They believe we have more in common with those universities than SEC members.
I do not see the University of Texas joining the SEC, ever. The main reason is that those who lead the university would greatly prefer to have it be associated with as many elite universities as possible.
Well, you rightly say, with Missouri and A&M now in the SEC, the SEC is at least as impressive academically as the remaining Big 12. While true, that misses the issue. Texas has inherited the Big 12, which fits its regional needs and desires very well. Those who run the university will not leave the Big 12 to make a lateral move in terms of academic rankings - no matter how much football might gain.
In addition, there is pride. The University of Texas is not going to follow the lead of A&M. The only way that Texas will be the newbie under A&M in anything as important as conference affiliation is if Texas has no other choice.
Texas may well prefer to keep the Big 12. But if it is going to leave, it is going to do so in large measure to affiliate with a larger number of elite schools. That means 3 options: ACC, Big Ten, Pac.
The Pac would mean Texas would take 3 other Big 12 schools. That would be a plus. The downsides start with playing games to your left in time, which is draining. It is much easier to go east than west in those terms. 2 members of the Pac Inland would be in Mountain Time, and then there is the 2 hour difference to Pacific time. The Pac is now #5 in national TV viewers in both revenue sports. Texas would lift the number in football, but not in basketball. The only 3 schools that would all help the Pac are Texas, OU, and Kansas. Would OU dump Ok St to make such a move work its best? While the Pac plays good baseball, nobody goes to games or watches on TV.
The Prince-like named B1G is the most homogeneous conference. It is the original conference about the largest state universities. Even Northwestern, its one private school, is very large by private school standards. The B1G, because of the size of the schools and the historic wealth of their states, is the wealthiest conference. But B1G football is historically a hot air balloon - all puffed up and easily burst when it encounters any meaningful opposition. Fans of every other conference see B1G football use similar labels for B1G football - boring, slow, predictable, dull, overrated, living on fumes from past glory. As can be seen by looking at B1G teams in bowls and against non-midwestern teams OOC and by seeing the demise of the MAC, midwestern football is on a continuing downward cycle, that I think will bottom, but never turn up significantly. That is the football reason ND is beginning the process ending its rivalries with B1G teams. We need to play in the south much more. The B1G cannot escape the midwest - ND can and will.
The ACC was third last year in the number of national TV viewers for football, ahead of the Big 12 and Pac. That is before FSU winning a national title, before ND begins play as a half member, before Pitt and Syracuse brought a decent number of northeastern viewers. What B1G people think is the huge weakness of the ACC is actually a strength that is certain to become even stronger. The ACC was second in basketball viewers. With ND (good numbers but not like football), Syracuse (easily the biggest draw in the northeast) and Pitt, ACC basketball numbers will move to number one. The ACC has the second largest number of baseball fans behind the SEC. Like the old SWC, the ACC is the most heterogenous conference, with multiple private schools as well as state schools, with very small schools and a couple of very large ones. The ACC geography would allow Texas to play directly to the southeast, northeast and midwest.