If the rumors of the Big 10 taking Stanford are true, they will be in position to put ND in checkmate at will, with Stanford, Michigan, and Stanford all in the Big 10, and once there's a clearer picture of how playing 8 vs 9 conference games factors in with the playoff committee, ND is about to have to decide between anchoring either the ACC, the Big 12 or joining the Big 10. It isn't in the Big 10s best interest for three of their members to play ND yearly. Especially when they expect two of those three to constantly be in the playoff picture.
The Big 12 is probably most balanced so the extra money from playing ND vs the chance of that one of those games being the difference of getting another team in the playoffs might not be worth it. The SEC, with OU and UT coming in, doesn't benefit from ND playing their teams very often either, leaving ND faced either actually becoming a true Blueblood and anchoring a conference, or joining one.
Speaking of playoffs, this PAC thing is going to put a wrench in the current setup. If they survive, the Big 10 and the SEC are not going to be cool with losing a playoff spot or two to a conference made up of UO, UW, the scrub Cali schools, Boise St, Hawaii Wyoming, SDSU, Fresno, San Jose, SMU, Saint Marys school for the Blind... If UO or UW can't go undefeated with that schedule, they should be banned from football for a year, so going undefeated shouldn't automatically be a playoff spot either... At least the Big 12 has legs to stand on. They have two recent playoff teams (one made the finals). UFC and BYU have shown they can play big boy football outside of fluke seasons. Baylor, TT, OSU, ISU, and WVU are not considered cupcakes by anyone's metric. It doesn't shock anyone when they beat good teams. They do quite often. But if the PAC dies (which is probable) it still changes the playoff auto bids. Either way, there will be some questions people will want clarification on as soon as the smoke clears out west