Proposed rule changes to allow flexible scheduling (rather than round robin divisional play) open up the possibility for basically limitless configurations.

Second, there is a lot of talk of adding an extra round to the playoffs. Considering the schools (largely falling in line with their conferences' wishes) propose and vote on these rule changes, which makes more money for the schools/conferences?

An extra round to the College Football Playoff, with revenues split between the CFP media partners, bowl hosts, and schools.
or...
An extra round of conference semifinals with revenues split between the schools and their media partners, cutting out the bowl organizing committees?

There's more money in it for the schools/conferences to handle the extra round intra-conference rather than as part of the CFP.

Those factors together really reduce the obstacles to forming MegaConferences. IMO, the possibility of a uniform symmetric 16 team/conference P4 is no more likely than the B1G simply absorbing the PAC to go to 24.