The reality is that Mizzou wants to go B1G. They always have. Their biggest rival apart from Kansas is Illinois. Mizzou gets tons of kids from Chicago, and St. Louis views itself as a little Chicago. They have little or no connection to the Southeast. Staying in the Big XII makes more sense than the SEC for Mizzou, and preserves the key benefits to KC as the hub of the conference, or at least co-hub with Dallas. I don't think the move is a slam dunk, and if Mizzou hadn't burned some bridges in the Big XII, I don't think they'd be seriously considering it. It may happen, but isn't easy for them.
As I posted yesterday, I think the conferences are coming to realize that there are only so many valuable properties out there, and that some of them are available. I think the Big XII sees WVU that way. If Mizzou stays, expect Louisville or BYU next.