My ultimate realignment proposal acknowledges we can't go back in time, but that we can go back by going forward.
Add teams so the SEC, B1G, and one other one (ACC-XII hybrid) has 20 teams.
Divide them into 10-team divisions, just like the conferences USED to be.
You play the other 9 teams in your division, under the larger conference umbrella.
Division-winners (who are true champions, by playing everyone else in their division) either go to the playoff or play a conf championship game to get in the playoff. But both get in.
If we have the SEC, that'd be UGA and Bama, B1G IU and OSU, ACC/XII Duke and BYU (although Duke wouldn't win a division in this format).
Six teams earning it, and maybe 2 at-larges. Clean, 8-team playoff, seeded however, with no rematches.
The point is, the 20-team SEC in this format could have the original 10 be in a division and all play each other, and the other 10 would make up the other division.
UF-UGA-TN-VAN-ALA-AUB-LSU-OM-MSU-UK
and
Tex, A&M, Ark, OU, MIZ, USCe, and 4 others who would do anything to be in the SEC
So UGA goes 9-1 vs their division and plays A&M who goes 9-1, both have tie-breakers over whoever and it all works out. Or they don't have a CCG and just go to the playoff, it doesn't matter. It's clean.
Yes, you're in the same conference in name only, but your DIVISION is the key. Same with the B1G - original 10 plus a division of the newer 10.