Agree. There won't even be a P3. Why would the B1G and SEC let another conference stand shoulder-to-shoulder with them when whatever form that other conference takes it won't even come close in terms of program quality or revenue.Sounds nice in theory, but the B1G and SEC will never go for it. And they shouldn't. Hate the SEC all you want, but the second place team in that conference is usually (almost always) better than the champ from the PAC 12 or ACC. The more deserving team should get in the CFP, not an arbitrary champ.
The one wrinkle I could see is if ND goes all-in with the ACC, they're able to hang onto Clemson, Miami, Florida St., UNC, and they form some kind of merged conference with the leftovers from the PAC.