Some (fairly) recent discussions regarding USC in all this:
USC's big choice: Big Ten, independent, Pac-12, or wait and see?
How an 18-team Big Ten could work in college football realignment world
Some of the talk centers around the concept of the B1G cherry picking USC and some other PAC schools (namely those in California to lock down the LA, SF, OC, and SD tv markets). USC bolting all the way to the SEC isn't out of the question--crazy things are happening now...
As long as the B1G keeps Ohio State and Michigan, they remain in a strong position.
The PAC-12, on the other hand, is in real danger of falling apart. USC could act like UT in our Big-12 heyday and really throw their weight around to gain big concessions--they seem to have that much leverage and a brand on par with peers like ND, UT, Bama, Ohio State, Michigan, and maybe 1-2 others. Out West, it's USC then a huge drop off.
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They'll likely be invited to multiple parties in this realignment.