Clearly, the Big 12 could have completed an expansion by now. They simply don't want to expand. G5 schools can't help them. By the end of their current media deal, the premier programs will have moved on from the Big 12, and the TV networks will offer peanuts to the remaining waifs.
They are likely trying to find a way to disolve their conference and find spots in P4 conferences for as many as possible. It may be futile. If they could agree among themselves, which is an incredible longshot, then multiply those odds by the even more difficult task of finding a distribution that would satisfy the receiving conferences. As time goes by, the willingness of Oklahoma and Texas to cooperate diminishes. Each year, the cost of departing gets lower. The lesser programs must all recognize that if they wait until the expiry, the events will overrun them. Only the big dogs will be in control of their own fate.
The SEC and B1G both want to land the better schools. Neither will want to compromise. This conflict, alone, could make any designed solution impossible. For the little players in the Big 12, money (exit fees from the others, i.e.) might get their buy-in. I can't imagine the amount of money it would take to get a concession from the SEC or B1G.
I think, because of the necessity for compromise, that the conference remains as-is until Oklahoma and Texas feel that the price for departure is bearable. Then, watch out.