Pac12 is a very good academic conference, right up there with B1G, there is zero chance they would ever consider Boise State for membership. If Super Conferences happen Boise would slip back to being a mid major. BYU would not be a good fit either for Pac12 as they already have Utah, about the only chance they have to survive is if the Big12 takes them.
Remember, any ideas you have for potential schools to join the B1G need to start with looking at the membership of the Association of American Universities (AAU). If they are not members of this Association there is no way the B1G considers them, the only exception would be Notre Dame. Syracuse is no longer a member and Boston College never has been a member so neither would be considered. If the ACC was to implode the B1G would likely go after UNC, Virginia, and Georgia Tech. No way B1G takes Duke, if these Super Conferences happen I could see Duke dropping football entirely as without drastic changes there is no way they can compete. Nobody at Duke would even notice.
Notre Dame would likely join the Big12 if forced to join a super conference. The Big 12 would be the only conference that would let them walk all over them like Texas does. The Big 12 would also go after ACC leftovers that the SEC and B1G do not want.
Pac12 stands pat unless the Big12 implodes, which means they struck a deal with Texas in order for this to happen. I cannot see the Pac12 going to far out of its geographic territory and they have complete control over who they take in the west, if they choose to.
If the SEC and B1G ever were to butt heads (ie SEC starts grabbing schools in B1G foot print) I could see the B1G making a run at schools like Vanderbilt and Florida. While the athletic dollars in the B1G may not be that much more (although that would be debatable) the attaction to the B1G would be its membership into the CIC which splits 8 billion dollars in Federal research grants. Unlikely this ever happens but who knows if the SEC was to take schools like Pitt and BC there would be some friction.
The Big East and the ACC would merge what is left and become a major basketball conference. They would become a mid major conference in football.