Although the B12 remains "fragile" to my eyes, I would not be surprised to see the B10 take UVA and perhaps UNC. On the other hand, travel would preclude them from taking Oregon and USC, as would California politics.
UVA and UNC are locked into their ACC contract for another 15 years or more. One would have to believe that every conference has seen all these schools jump conferences over the past decade and written into the new media deals regulations that make it nearly impossible or very expensive for a school to leave and join a new conference. For those that say that a good lawyer can always find a loophole, then I would ask, "then why are OU and UT still in the conference?"
Both schools along with ESPN hoped that when the deal was announced, that the other 8 schools would panic and try to find another conference to jump too, and ESPN had already told the AAC to reach out to the schools, hope they would jump, thereby freeing OU and UT to join the SEC. Bowlsby finally got off his rear end and shot that letter off to ESPN telling him that their back-channel deals with UT, OU and the SEC broke the contract, and if those schools left, then ESPN would not be able to lower payments to the league for their media rights package, and that the schools would still have to pay a large lump sum payment for leaving the conference.
It's important to remember that when the remaining 8 schools were asked to again pledge the GOR rights to the league, that ISU and the 2 Kansas schools refused to do so at this time. If UT and OU cannot afford to buy their way out of the league, no way could ISU and the Kansas schools come up with that type of money.
OU and UT are going to leave the league, when that happens, no one knows, but until that is cleared up, and the Big 12 knows how much money each school is going to make from their TV rights, then no expansion is going to happen in any league. You also have to remember that with the conference growing from 10 to 12 teams, the numbers will have to go up overall for the league to be able to match what it currently is paying out to each school. Granted there will be a delayed time until the four new schools get a full share, but 5 to 8 years down the road they will.