You assume ND will join when the ACC GOR expires.
I’ve thought that as possible since Texas/OU left the B12 and that going national should be the B10’s response. Go national and have many of their rivals in conference and wreck their current home a bit and then you have a good shot as you’ll get at ND. However, I’ve never taken that as a given just possible.
I don’t think money will ever be an issue for them. CFP access likely won’t be either. I think a home for its other sports is one possible issue for them. The other is scheduling in general if conferences ever increase the number of intraconference games they play. So it depends on what ND leadership thinks is a suitable enough home for their other sports. Will leftovers of the ACC or the B12 be good enough or not? I don’t know.
I think a lot would depend on whether the SEC joined in and took any ACC teams. If they don’t, I think ND could stay with the 12 leftovers. If they do then the 10 or less leftovers might not be as attractive. Maybe the SEC doesn’t join in an ACC raid just to lessen the probability of ND coming to the B10. So in my mind, the B10 can increase its chances but it’s still not a given.
If ND comes on board then I think you can go to 22 or 24. If they don’t, then I think stopping at 20 is okay and having 4 in the west, 5 in the east and the rest in the middle. You could have 4 divisions of 5. Nebraska might have to be grouped with the west and then you can have conference semifinals too for more valuable inventory.
If it’s too much for any one team, maybe you could even rotate annually the team from a specific group that rotates as part of the west.
Just me speculating .without anything to back up my opinion
I really don't see expansion ending until there are only 2 top powers .
Conferences limiting their numbers when there are still quality programs to poach and be the #1 is something I don't see.
Getting the biggest deal is what I see the B1G and SEC trying to do for bragging rights and control of the college sports world . or at least be considered the best of all and paid like it.
As for Notre Dame, like you I feel they value their independence in football and consider that a major part of having a national fan-base and won't be giving that up unless forced to because they'd lose too much money by being an independent.
I feel they are locked into the ACC until 2036 and when that year is reached the B1G will go hell-bent for leather after them.
But the B1G knows getting them won't be easy so ot will take over the West Coast first , keep control of the midwest, then fight the SEC for the south by adding ACC schools to it's eastern presence and have a east/south division
with or without ND joining it's MidWest programs.
The number of ACC programs the B1G poaches will be one more if ND stays independant and puts it other programs in the Big East or 1 less if ND goes B1G.