There is no way they add a team that doesn't bring more money to the conference. They don't want dead weight. So their decision will primarily be based off of how much money can "X" school bring to the conference. BYU is in a great position for this because they bring a bunch of eyeballs to TV sets and have a national fan base. They also have one of the larger stadiums. If they were added to the Big12 today they would have the 3rd largest stadium behind only Texas and Oklahoma.
After money, then they will start to consider secondary issues like geography and such, but money is king.