BE has long advocated CSU... I can tell you, with certainty, they won't make the cut if the Big 12 only goes to 10 or 12.
BYU and UCF are the slam dunks, that's obvious.
The service academies do not make sense. They literally are NOT TRYING TO COMPETE AT A HIGH LEVEL! What do people not understand about this? They play sports, but their mission is creating soldiers and leaders first and foremost. That is never going to change.
Just as one reference point, recruiting: The 247 team talent index has Navy, Army, and Air Force at 140, 150, and 200th respectively amongst the 230 schools they track nationwide. Regardless of their ability to use unique systems to improve on field performance and the ability to get some eyeballs on otherwise bad teams/games, they are not a fit for any serious football conference.
If the new Big 12 wants to be at all serious about playing football at a high level, you either need to literally be TRYING to do that, or have Kansas level basketball influence. None of the academies are even in the ballpark.