The same thing would happen though.
The ACC would poach out of the other conferences, not the other way around.
It's going to be a matter of what's marketable - would you rather play for a conference that has a core of:
Boston College, Syracuse, Wake Forest, Georgia Tech
Iowa State, Kansas St, TCU, Baylor
Washington St, Oregon St, Stanford, Cal
(namely leaving out schools like Pitt, VA Tech, NCST, Louisville, KU, OSU, 4 corners, UO, and UW for obvious reason).
I think this is the thing that ESPN is missing - the core of their new ACC as well as the Pac 12 is completely trash. Stanford and Cal isn't nearly as marketable as they want everyone to believe, Stanford being interesting only if they can tie them to Notre Dame. Meanwhile, that core for the Big 12 is solid, no matter how much ESPN wants to play it off as trash. I think FOX sees that, which is why I think they'll try to push as much of the Pac 12 to the Big 12 as possible.