If the Pac-12 collapses, I think you wind up with four 16-20-team superconferences that will each have a seat at the table. Four conference champions work easily into a four-team playoff with the conference championship games serving as the de facto quarterfinals.
In my dream scenario, the Big Whatever lures Notre Dame from the ACC. The Big 10 has always made more sense but the Irish remember decades ago when they wanted to join the Big 10 and was told they'd never approve of a Catholic school in their conference. Notre Dame has never forgotten that.
Notre Dame would be the only "whale" left with national visibility. The Big whatever can add Oregon and whichever two other PAC-12 schools to get to 16. you'd then have (West to East) Oregon, PAC1, PAC2, BYU, Texas Tech, Kansas, K-State, Okie State, TCU, Houston, Baylor, Iowa St., Notre Dame, Cincinnati, West Virginia, Cent. Florida.
ACC can stay as they are and maybe find two more schools to add, possibly Memphis and UAB. If they want to have divisions, they can do that or if they just want to have annual rivalries plus the "best 2 teams" championship game, they can do that.
I miss the old Mile High Stadium.