I don't see it. UNC is THE prize next to ND. And I think UVa might be next. Not so much about new markets alone, as it is new markets plus recruiting plus non-dilution of current product plus academics. Perhaps they even go as a package as they are rivals.
If so, there are two scenarios:
(1)... the B1G gets UNC/UVa... the SEC has to decide whether to add duplicate states to its portfolio... perhaps they go for all 4: FSU, Clemson, Louisville, and Ga Tech. Now all in-state matchups are conference games. 9 P4 Game problem solved. Sorry, Oklahoma State.
(2) the SEC gets UNC/UVa... and the B1G has to decide what to do next. I could see them doing nothing. I could see them adding Florida State and Clemson. It would be interesting to see if Texas Tech could sneak in ahead of Clemson. Huge investments being made there. That would get the B1G into Florida and Texas, which might be big for recruiting. Recruiting might make Georgia Tech a sleeper as team #2 also. But, assuming the B1G goes FSU/Clemson... it is less certain that the SEC would make any move to go beyond 18. Would Ga Tech/Louisville move the needle enough financially to do anything? Would the SEC want to add Colorado, Arizona State, or Kansas just to get to 20? I doubt it.
In any scenario where the ACC loses 6 or fewer schoosl, there would be a path forward. 20 teams in the B1G/SEC each is not enough to destroy the B12 and ACC. There would be enough left to maintain each conference. And if there is a scenario where the B12 loses a few schools, it looks all the better for the ACC to maintain equality with them.