I think after seeing the above I think the B1G ideal would be to add Washington, Stanford, Colorado, Kansas, Baylor, Pitt, UVA, UNC, Duke, GA Tech, Miami, Notre Dame.
Then have divisions of...
Washington, Stanford, USC, UCLA
Colorado, Nebraska, Kansas, Baylor
Minnesota, Wisconsin, Iowa, Illinois
Michigan, Michigan State, Indiana, Purdue
Ohio State, Penn State, Rutgers, Maryland
UVA, UNC, Duke, Miami
Northwestern, Notre Dame, Pitt, GA Tech
That allows you to play everyone once every 4 years, one team twice every 4 years, and you keep 4 yearly rivals. IMO anything over 28 teams makes it nearly impossible to schedule. It becomes too big.
So looking at ND's top 10 teams played...
Yearly: Navy (OOC), USC, Pitt, Northwestern, GA Tech
Once every 4 years: Purdue, Michigan State, Michigan, Stanford
Not on schedule: Army (could add yearly OOC)
Expanding to their Top 20
Yearly: None
Twice every 4 years: Miami
Once every 4 years: Indiana, Iowa, UNC, Penn State, Wisconsin, Nebraska
None: Air Force, BC, Carnegie Melon
So it would be a national conference which allows for a national schedule. Of their Top 20 all time played opponents 15 would be in the B16. One team no longer plays football. Another team they would play OOC every year. That leaves one OOC game which they could rotate between BC (Boston) and Army (NYC). Which means over a four year period they play all but Air Force from their Top 19. They can also play the Navy game in San Diego or Houston to add more games in those two states.