The only way I see that happening is if the Big 12 ends up being raided, and they still may be at some point, and a few more teams from the Big East get raided.
Then, I could see a scenario where the 4 remaining strong conferences (Pac 12, SEC, Big 10, ACC) form an alliance and break off to form their own division of college football, and they make it a requirement to have 16 teams with some sort of conference playoff format prior to a national playoff.
It would take some cooperation, correct, but I think if the money were right and the Big 12 and Big East were weak enough, you could see that cooperation take place.
The money associated with a playoff would be huge, and seceding from the NCAA could mean those schools keep a lot more of it.
I just don't know how it would work out though. The Pac-12 obviously made overtures about Texas, Texas Tech, Oklahoma, and OSU. If they did that, they'd be at 16. The SEC has A&M. Would we go for Missouri next? If we needed to add two more, where would we go for those? If we're in theoretical collusion with the ACC, we aren't stealing UNC or Va. Tech. We'd have to go for West Virginia or someone like Louisville or Cincinnati.
The ACC is at 14 now, who else would they add? Rutgers and Syracuse were rumored to be making a push for joining their league. If those two, who does the Big 10 get? Would it finally be able to force Notre Dame to join in this hypothetical? Then do they go after UConn? That's the issue. Even if you had cooperation and asked each league to get to 16, you'd have a battle over those remaining pieces. The Big 10 and SEC would probably both want Mizzou. The Big 10 and ACC both would probably go after Syracuse. The SEC might cave and go after Oklahoma and OSU and fight the Pac 12 for them.