Not sure about the SEC or ACC schedules, but the B12 CCG is scheduled for 12/12. So the B1G playing a CCG one week after, would still work out okay for the post-season selections and plans.
We might even see some of the conferences that are already playing, insert another bye week somewhere in the season, to make it align exactly.
Edit: Just checked and the SEC is already scheduled to play its CCG on 12/19 so it should work out fine. I wouldn't be surprised to see the B12 push its CCG back a week to allow for an additional bye during the season.