Realistically, conferences aren't shrinking, just being plundered or growing. I'd do a 16x4 setup, with pods, so each incoming FR class will play everyone else in their conference twice - once home, once away (every other year).
SEC + 2 (KU, OKST)
B10 + 2 (UVA, UNC)
PAC12 +4 (BYU, TCU, OU, Tex)
ACC -2, +4 (ND, WV, KSU, UCF)
So existing P5 programs ISU, TTU, and Baylor fall by the wayside. ND and BYU are included. The XII and ACC are poached, but the ACC survives.
Each conference has four pods of four schools each. The PAC catches up with the SEC and B10, thanks to UT + OU. The ACC becomes the red-headed Frankenstein ACC/XII combo + ND.