My opinion is unfortunately it takes two to tango. Penn State hasn't supplanted anyone in 25 years. In the west we'd be behind these teams in the mind set of opponents.
Iowa - Wisconsin, Minny, Illinois - cross div MSU, Mich
Minny - Iowa, Wisconsin - Cross Division - Michigan
Wisconsin - Iowa, Minny, Illinois - cross Div - OSU
NW - Illinois, Iowa, Wisconsin
Illinois - Iowa, Wisconsin, NW, Purdue, Cross Division - Indiana and Ohio State
Purdue- Indiana
Can pick anyone we want, but as we know a true rivalry transcends the cyclical nature of who's good or bad in a snapshot of time.
The B1G was a good move, but this part is the worst part of it. History isn't helpful in this aspect when they have been playing each other for over 100 years, in all sports, and their alumni have worked with each other (in big numbers) in markets like Chicago, and others.
Over time, barring more expansion or shakeup its going to be the the triad of Iowa, Wisconsin and Minnesota.