I give BYU's chances of getting into the Big 12 at 80%+. Bowlsby in June announced the CCG scheduled for 2017 season, and during the news conference yesterday he mentioned they could add teams by next year, which would help the CCG schedule. This is only one of the reasons I see BYU as being in, the Big 12 could get two teams already in other conferences but I don't think they would want to pay two buyout exit payments, so with BYU as one of the teams, they would only need to pay one exit fee.
I think what the Big 12 did in the news conference yesterday was extremely smart. They started right off talking about Baylor and went into talking, very cryptically about expansion, never actually coming out and saying they were going to expand but they are taking the next step into looking at expansion. What this did was very effectively take the spotlight off Baylor and directed all the media's questions about expansion and what are they really going to do, expand or not.
So with that I am saying Big 12 expansion is 100% and BYU's addition greater than 80%! 8)