A few thoughts... as todge already pointed out this wouldn't be happening in the near future. This possibility is 6-8 years away. So unless there is some kind of BIGXII Armageddon it will be sometime before anything happens.
As far as who would and would not be considered we need to consider research money, AAU status, new markets, and on the field success or potential.
All religiously based schools are out, so no BYU, Baylor, SMU etc.
Every school that isn't getting big time money for research is also out Boise state, UNLV ...
Finally the PAC is not going to go after schools that are in small markets and far away. I'm looking at you Hawaii, it's not happening.
So if it were to happen in a few years from now the schools they will consider IMO are
Texas, Oklahoma, Kansas, TTU, KSU, ISU from the BIGXII and in that order.
Houston, Colorado St, New Mexico from the G5 also in order.
I do believe they would consider Oklahoma state and TCU if they were in some kind of package with some of the above BIGXII schools.
Should be highly entertaining to watch over the next decade, and have fun guessing