It really doesn't behoove the B1G to expand much more beyond the current 16, although if ND is pressed to join a conference then the B1G makes the most sense and it does move the dial from a $media$ perspective.
Yes, I could understand adding at least 2 more west coast teams for anchoring that part of the country and for travel partner considerations...so UO/UW would be the apparent targets. You then would need 1 more addition to level out the conference at 20 ...(imo that would be a school like Stanford due to it's rivalry with ND and it's academics/research)... but then I think they stand pat.
Yeah, if/when the ACC implodes you can talk about getting a footprint into Florida by adding Miami....but then you'd almost definitely need at least one more southern school to act as travel-partner. Who would that be? FSU? Clemson? GaTech? None of them really move the dial, although I guess GaTech and the Atlanta market could possibly make them viable. The real gem for any future ACC poaching is UNC. They have everything the B1G is looking for, but I doubt they would be as interested unless you also bring in one of their historic rivals like Duke or Virginia.
Lots to speculate about for sure.