Regarding the OP, any of those 3 moves would, in and of itself, constitute a major move in college realignment. I think scenarios 1 and 2 would certainly produce a corresponding ripple effect, but not scenario 3. To the contrary, I argue that scenario 3 (ND > ACC) would produce a dampening affect on realignment as it would stabilize the ACC, by mollifying FSU, and likely usher in a GOR. Having said that, I think only scenario 1 or 3 is likely, and of those two, scenario 1 is the most likely.
First, scenario 2: Texas and Oklahoma > PAC. Texas and Oklahoma are going nowhere for roughly 13 years due to the GOR. The only way they could escape the GOR would be a for a majority of B12 schools to vote to disband the league. Not happening. Furthermore, truth be told, I think both Texas and Oklahoma are serious about rebuilding the B12, and therefore have no hidden desire to leave the B12. I don't think scenario 2 is particularly realistic, due to the GOR and lack of motivation, and further consideration is unnecessary.
Scenario 3 -- ND "all in" to the ACC -- is, IMO, relatively unlikely due to the fact that ND remains fiercely protective of its "football independence". ND to the NC game this year will, I think, only reinforce ND's independent mindset.
Ironically, ND's association with the ACC, but not joining the ACC "all in", is, IMO, the cause of the B1G's recent movement in expanding with MY and RU. Rather than stabilizing the ACC, ND's mere association with the ACC has spurred Delany into damaging the ACC, removing whole chunks of the Northeastern Corridor from ACC influence, in an effort, I think, at least in part, to show ND the "error of its ways". The ACC may have let the wolf into the henhouse. Delaney may not be done either. If just one more ACC school is poached, then ...
Scenario 1 will almost undoubtedly be ignited. It is no secret that the B12 lusts after Florida State. And while the B12 understands that the SEC is not interested in FSU, FSU understands that they can slow-play the B12 just in case the SEC changes its mind, or, in case, by some minor miracle, the B1G comes calling (if the B1G should go all the way to 20 at this point in expansion). Furthermore, logically, since the ACC contract is at least 20% less per year than the B12 contract, FSU should be in a hurry to join the B12. But FSU isn't in a hurry. They are run by human beings and human beings are inextricably bound up in emotions. FSU has an emotional attachment to the ACC. Call it loyalty. Call it whatever you want. But FSU still appears to hope the ACC can be made to "work", the money be damned.
However, if the B1G removes one more top tier school from the ACC, as a result of Delany's wrath toward the Domers, FSU may reach a critical mass where logic finally trumps emotion. If and when FSU leaves the ACC, a wholesale run on various schools of the ACC will certainly ensue. Any one of the various doomsday scenarios viz-a-viz the ACC that we read and hear about could occur.
If FSU bolts, my guess is that, in the end, both Virginia schools will be gone, 2 or 3 North Carolina schools will be gone, GT will be gone, both Florida schools will be gone, and Clemson will be gone. The ACC will go on, but only as a mere shell of its former self. Louisville will be sorely disillusioned.
Yes, I think the key is FSU. However, I don't think FSU will be next. It will take the B1G or the SEC to pluck one more ACC school, which will cause FSU to give up the ghost, and it will probably be the B1G that launches the avalanche. If it happens, the ACC could be depopulated in a matter of days because there has already been a lot of undermining of the ACC foundation that has already occurred over the past several months.
I really think the B1G wants UVA, not necessarily Georgia Tech, and Delany is stalking GT to try to flush out his target in the South: UVA. OTOH, maybe the B1G is serious about GT, who knows? I think we'll find out a whole lot more in the next several days. Not weeks. Not months. But days.
As for me, a Texas alum, I'd be tickled to no end if Guy Jones prediction for the B12 came to pass: Connecticut, Florida State, North Carolina, Clemson, Duke, and San Diego State. Add them to the existing B12 and you'd have a helluva league there.