My uninformed take is that Missouri would prefer to move to the Big 10, but isn't going to get invited. So, Missouri looks at the options - SEC or staying put in the Big 12-3 = 9.
If Missouri were to go, then it's scramble time for the Big 12 and their geographic proximity would suffer, as they'd have to expand both east and west, and be missing a cornerstone state in the middle of their region.
I see why the SEC would want to push north and get into the St. Louis and Kansas City markets more than West Virginia, even though WVU is probably a better fit culturally in the SEC. SEC wants to get beyond the "NASCAR market" that they currently hold. Missouri helps them more than WVU in that regard.
In any event, the Big 12 can't stay at 9 teams. They have to add someone, and probably would need to add 3 to get back to 12 for TV, over Texas's perceived objections and not wanting to have to play a conference championship game. Those days are soon going to be over for all the BCS football conferences.
So, either WVU or Missouri to the SEC. I think they stop at 14.
Big 12 has to take a few schools to beef up from 9 - or 8. I think they pick from among TCU, BYU, Louisville and Cincinnati. They are way too Texas oriented already, but TCU is a really good football team. BYU is a little distant for travel w/out Nebraska and Colorado in the league any more. Boise State is even farther and is not a major player in non-football sports, to the best of my knowledge. Cincinnati is also pretty far from the conference's center of gravity, more so than Louisville, so that may count against them.
The more I think about it, the more I think Oliver Luck is still lobbying to get WVU into the SEC and hasn't succeeded yet. That might point to Missouri getting an invite to the SEC first. But would Missouri look at a move to the SEC as a step down academically, despite the extra $10M a year in sports revenue? They might.
I'm also very relieved at the reports that Va Tech turned down an SEC invite. Sources say the whole Va Tech vs. Virginia rivalry and state politics will keep those 2 in the same league and the SEC will never invite Virginia. What this also shows, though, is that the SEC is willing to try to unlodge an ACC team. Florida State might be next on the wish list before Missouri or West Virginia.
If I'm West Virginia, I'm on pins and needles thinking that I'm the third or fourth choice to get into the SEC.