Not to go all Legends and Leaders, but I don't think divisions need to be geographic, nor actually fixed in terms of composition.
I like the idea of divisions becoming more loose and malleable. With conferences becoming larger and games between interdivisional foes becoming increasingly rare, I think the concept of divisions themselves needs to change.
Have a group A and a group B, mix them up every 2 years (after home-and-homes between all the division members) so that everybody in the conference plays everybody else multiple times within a four year window. Sure, it has a downfall of basically needing to look at the league standings to know who is in what division from year to year, but then, so what. You should want to see Alabama vs. Florida, Nebraska vs. Ohio State, and Clemson vs. Miami (just to pick a few matchups) more often than it happens now. In membership terms, I already know that northern ACC schools want to see certain southern schools more often, which can't happen with fixed divisions, and I'm sure the same is likely to be true in the Big 14 and possibly the SEC.
That, or just blow up the mega conferences and get down to a manageable number and play everybody every year, like the Big Actual 10 accidentally did.
