Probably so. And when the time comes I wouldn't be surprised if the same happens when Michigan and Nebraska visit.
Northwestern probably faces the same dilemma, they scheduled an Illinois game for Wrigley, which ironically seats less, atleast baseball-wise. I can't seem to recall them rescheduling one for Soldier Field atleast recently, maybe they have?
I could see MD doing it more likely for Michigan, heck I'd say Penn State would be more likely than Nebraska if the demand was there (assuming they aren't too hurt from the scandal if the program falters). For Nebraska, they'd probably have to see that 20k+ Nerbaskans would travel for that game.
I think they'll always schedule 6 home games, if they have a 7th I can see it.