This is all about ND. Once they commit the other pieces will fall. If they do not, there will be unrest in the ACC, and it will leave open the possibility for defections.
if ND joins ACC, it is stable, and B12 is in trouble. if it joins B1G, they are done, and ACC is picked apart.
The only reason Notre Dame would go full membership ACC over B1G is spite. But you're correct in how it will happen and we've seen schools make conference decisions based on spite already.