SEC wants TA&M along with OU badly. They tried to get them this year while Texas was pushing for the PAC10, but you just didn't hear about it as much (atleast in Ne you didn't, but here in Oklahoma you did).
If the Big10 can get N.D. to finally commit, I can see them maybe taking Mizzou to make it an even conference. And then your mentioning of the super PAC16, which I am sure they will take whoever they can get ahold of (I mean they did take Colorado of all teams). I know it is a big IF, but IF OU cuts ties with OSU, they will leave and go to the SEC. I know it will never happen (cutting ties that is) because of the on going politics here in Oklahoma with the two teams.
Also I am sure the weaker teams in the Big12 were offered a bigger package then they are receiving now, they would leave without hesitation (again bringing CU back as an example).