Here would be a potential Big Ten schedule as a member of the Legends Divison:
Army/Air Force/Boston College/rotating game against any other non-league team ND wanted to schedule
Penn State/Ohio State/Indiana/Illinois/Wisconsin/TBD 14th league team. - This would be a rotating conference game each year against a Leaders Division team, including whomever would be the 14th league member.
If the Big Ten remained at 8 league games, it seems like a perfect fit for Notre Dame being able to join the conference AND maintain traditional football rivalries. You could create the schedule so that Notre Dame always begins and ends the season with Navy, USC or Stanford. You could have Notre Dame - USC in the final week with Ohio State - Michigan, Nebraska - Iowa, etc.
The only flaw I see with this plan is that all non-league rivalries would require home and away games, meaning Notre Dame would not have a 7th home game in any given season under the traditional 12 game season. But with the way college football is about big money any more, it might be realistic that the regular season is expanded by 1 or 2 weeks in the future.
The only question I cannot answer would be who to add to the Leaders Division to balance out the divisions that would be on par with Notre Dame to keep the Divisions as evenly competative as possible.
Other than the protected crossover with Purdue, the rest of the Leaders Division would play ND twice every 12 years. That would add change to the schedule and provide for some intriguing matchups that are not year in and year out.
Besides current rivals Michigan and Michigan State in the Legends Division, Notre Dame could have an instant rivalry with Northwestern in all sports as Northwestern is also a private school and would be a great regional rivalry for Chicago. Nebraska would be a huge yearly matchup, and ND does have some long ago history with the Cornhuskers, as well as Minnesota and Iowa.
I think its safe to say that most - if not all - of Notre Dame's games would be on ABC or ESPN - or whomever acquires the rights to Big Ten games in the future. The Big Ten Network would be there to air replays of the games.
I also think its safe to say that both Notre Dame and the Big Ten will greatly increase revenues if this played out.
Again, these are only my thoughts. Not saying it will happen, but it all just kind of hit me when looking at Notre Dame's schedule and realizing what could happen by placing them in the Legends Division with a protected crossover game against Purdue and including the Big Ten - PAC 12 arrangement that will happen in future years.