I think those "duds" are on thin ice. For the P5/4 conferences, athletics is a business. Generally, they aren't going to accept just anybody. Only a small handful of schools can enhance the bottom line of the P5/4. The Big 12's nonexpansion is evidence of this. The PAC might be willing to take some refugees from the Big 12 in order to have a presence in the Central Time Zone. And that is a stretch.
Its not only the P5/4 conferences. The TV industry would also prefer to buy media rights from WVa, Texas Tech, etc. at G5 prices, rather than P5 rates. So where is the impetus to include more teams in the P5/4? I predict that after the Big 12 splinters, there will be fewer that 60 Px programs.