I'll try to do this slowly so you can follow as when things are presented at a normal pace it appears to be beyond your capabilities.
1 - A&M does officially move to the SEC, leaving nine remaining members of the B-12.
2 - The P-12 takes four of the remianing nine (just to keep you up to speed, current ten as although they are called the B-12 they only have ten members, less A&M) to expand to sixteen.
3 - Likely in two steps (one to get to fourteen, the second to get to sixteen) the SEC finds another three schools to add to their conference. For the sake of argument, I will project what appears to be the worst case for the ACC, which would be three members of that conference jumping to the SEC.
4 - The ACC will immediately grab BE schools to replace those that they lost to the SEC and later add other BE members when they move to sixteen.
If this was too fast for you I apologize but I constructed this in a manner which a fifth grader should be able to follow with ease.
The thing is, as a 16/24 model would be beyond anything that could be considered realistic, among the few certainties is that the BE will not be able to start with its own (nine members once TCU joins) football membership and increase to sixteen. Another certainty is that the P-12, B1G and SEC will all survive this round of expansion (to four super conferences). This will leave three players remaining for the last one spot (as a superconference), the B-12 (which will be nearly completely decimated by this point), the Big East (which will be limited in what it can expand to without a split from the catholic schools) and the ACC.
As a hybrid BE cannot get to sixteen, it will be obvious to all that they cannot be a final destination. This will not only make the ACC a more attractive landing point for football members who want to remain part of the BCS, this will by default make them the fourth superconference.