With the break-up of the old Big East, Notre Dame had two major concerns: finding a big-time home for all their sports besides football and having access to premier bowls for the football team. Those were the two levers that I felt at the time would drive ND into full membership into the Big10. If the ACC had not thrown Notre Dame this lifeline, I believe that ND would be in the Big10 today. Since the ND and ACC agreement has been extended through 2037, what possible carrot or stick could the ACC have to pressure ND into bringing their football team into the conference?
There is only one stick left that could force ND into full conference membership. That stick is legitimate access to the playoffs. As of today, Notre Dame has that access. A 12-0 ND team is almost assured of being picked and a 11-1 ND team has a good chance to be chosen. However, if the playoff rules are ever adjusted to favor conference champions to the extent that ND is forever precluded from being chosen, then you will see the ND football team in the ACC.
Could the playoff rules be so adjusted? Perhaps, as there has been a lot of complaints from some in the Power-5 conferences that Penn State was the Big10 champion, yet was passed over by the selection committee for Ohio State. I can definitely see the committee being told that extra weight must be given to conference champions.