from market size to actual eyeballs/subscribers between now and then (granted, a big assumption):

B1G: Kansas and Missouri. Kansas attempts to shoehorn K State into the deal, but the B1G won't budge, giving them a "take it or leave it" ultimatum (to which the Kansas state legislature reluctantly acquiesces). Mizzou's happy in the SEC, but I still believe they would leave for this opportunity (plus, no GOR in the SEC).

SEC: Oklahoma, ok state, and West Virginia. Alabama and Auburn slide on over to the east, while OU/osu/WVA take up residence in the west. No objections to grabbing two schools from the same state, due to the assumed change in cable model.

Texas: backfills the Big 12 departures with other Texas schools (Houston, SMU, etc, and possibly BYU), while waiting out the longhorn network contract. ESPN rebrands the longhorn network into the Texas network (against the objections of the remaining non-Texas schools, but what are Iowa state/K State going to do about it?).

PAC: does nothing, for the time being. Content to wait until the longhorn network ends in the 2030's, with no desire to add anyone like BYU, Boise, UNLV, or anyone else until Texas is available.

ACC: does nothing, for the time being. Content to wait and see if Notre Dame will become a full-time member (a decision I honestly don't think the Irish will ever make, but I could easily be wrong).

So, not exactly clean or exact P4, but a massive amount of change, nonetheless.