A few thoughts:
(1) GORs *might* be breakable in theory. I can provide several hypothetical legal arguments to break them. However, in practicality no one that matters WANTS to challenge them (and it's a huge grey area at best as whether a challenger would ever win). It always puzzles me whenever I see comments that the Big Ten would be the conference to try to break the GOR agreements when that conference INVENTED them for college sports rights purposes. They first put a GOR into place back in the 1980s - over 20 years before any other conference figured out their value. Believe me - Jim Delany and the Big Ten want those GORs to hold up.
(2) The reason why GORs are powerful is that if a school leaves a conference with a GOR, that conference retains such school's home TV rights AND the school will no longer receive a dime from that conference. That means that the poaching conference effectively only gets the rights to that school's road games and, as such, the new conference isn't going to pay the school a full share for that. So, if the school doesn't get paid for its home games from its old conference and it's not getting a full share from its new conference, there's no way that they're going to move (at least between P5 conferences). Once again, seeing that 4 of the P5 leagues have GORs (including the Big Ten and ACC), no one wants to challenge them in practicality even if there are possible legal arguments against them.
(3) The Big Ten isn't going to have an odd number of football members with the current NCAA rules for conference championship games. The pre-conference championship game odd number of members at 11 is irrelevant. Now, if the NCAA rules change where you don't need divisions for conference championship games, then that provides a bit more flexibility to have an odd number of members.
(4) It's pretty safe to state that each new school that comes to the Big Ten needs to generate at least $40 million in conference-level revenue annually just to break even... and no one expands with the intent to just break even. I don't know if $100 million per school in additional revenue is required, but it's certainly reasonable to believe that the Big Ten would be seeking $100 million total from 2 schools being added.
(5) Very few realignment decisions are as easy as "Adding School A means delivering X number of cable households at Y dollars". If making money was that clear cut and easy, then it would have been done already. The thing to remember is that it's NOT that clear for leagues with conference networks outside of schools like Texas and Notre Dame. Rutgers, for instance, is a major risk for the Big Ten. Depending upon how you view it, if they aren't successful in getting solid BTN carriage in at least New Jersey, that could sour the Big Ten's view on the NYC market completely. (Maryland is much less of a risk, regardless of what the ACC partisans will try to argue, which is why, not surprisingly, they got a much better deal upon joining the B1G.)
(6) Further to the last point, the NYC market may end up being TV fool's gold for everyone in college athletics. Even if a league were able to combine Penn State, Notre Dame, Rutgers, Syracuse, UConn, Michigan, Ohio State, BC and Miami all in the same conference, that would STILL not guarantee basic coverage in the NYC market. The main thing that the Big Ten can really bank on with the Rutgers addition is that it's a very good football recruiting region for the North and "normal" student recruiting area for people that are willing to pay out-of-state tuition (see the fairly high matriculation of NJ residents at places like Michigan, Wisconsin and Indiana considering the distance, much less closer locales like Penn State and Maryland), which is how public universities across the country need to increasingly be funded.
(7) As much as it pains me, I agree with Terry D regarding Notre Dame. From the Big Ten perspective, the only thing worse than ND refusing to join the Big Ten is too see them actually joining the ACC (or anyone else) as a full member. As a result, ND will not be "forced" into a conference by outside forces, *especially* now when it has an agreement with the ACC. Even the SEC isn't interested in seeing the ACC strengthen itself with a full member ND - that move could get the ACC up to the Big Ten/SEC-level in terms of revenue and the SEC would be negatively impacted with that strong of a league that they directly compete against in their region. Everyone wants ND to join their *own* conference, but they have no interest in seeing ND joining a different conference outside of their own.
So, they'd rather have ND be "Switzerland" and maintain the status quo as an independent than to force them to do anything. Just look at how much deference all of the P5 conferences gave to ND over the past couple of years regarding the CFP playoff and related issues. Who did they choose to make the CFP announcement? ND AD Jack Swarbrick. When the Big Ten and Pac-12 were working on a scheduling alliance (which eventually fell through), they told NO ONE about it before it was announced... except for ND. When the Big 12 and SEC were working on their Champions Bowl (which was eventually awarded to the Sugar Bowl), they also told NO ONE about it before it was announced... except for ND. Make no mistake about it: ND is in with in crowd and always will be (whether it's out of friendship, fear or straight up business).
