What does the Big 12 gain from it? Enough teams to hold a Conf Championship that would amount to a Texas - OU rematch most years? Would it bring enough TV revenue to distribute more $ to each school? (we know Texas and OU won't be taking pay cuts, that's for sure).
People think of expansion as pieces to puzzles more than they think of what would actually benefit everyone in the league. I wouldn't be surprised to see the Big 12 become the Big 9. Unless they think Mizzou is already gone.