This 'alliance' was a perfect time to have all of these conferences get to an even number of teams first and foremost (14 or 16).
In football, all have 8 game conference schedules, and 1 game/season against each of the other 2 conferences (1 Home and 1 Away), and your 12th game to do as you wish or against your biggest out of conference rival.
So, example- Ohio St.- 8 BIG 10 games, home vs. NC State (ACC), at Utah (Pac 12) and 2 games for their own.
Clemson- 8 ACC games, home vs. UCLA (Pac 12) at Iowa (Big 10), 1 game on their own and rival S Carolina
This would boost cross-region interest. Also can still schedule an SEC school in there, etc.