I've read the rumors of BYU and Air Force going to the Big 12, but I think chances of that happening are slim to none. Big 12 officials have publicly committed to a ten team conference. The proposed TV deal that saved the league was agreed to by the remaining ten schools who I doubt want to divide the pie by 12. I doubt BYU and Air Force or any other school for that matter that the Big 12 can add enough to the Big 12 TV pie to make it convince the remaining 10 to expand.
And as I am writing this the guy from orangebloods is on Cowherd and he said the Big 12 is set for 10 years and the schools took a "blood oath".