Notre Dame joining the ranks of the Big Ten could and should happen. Think about it, Notre Dame all ready plays the likes of Michigan, Michigan State, and Purdue. And those games are usually hard fought games.
Also Notre Dame has their contract with NBC and it would help the Big Ten get even more exposure then they currently are getting. Even though they all ready have games on ABC and ESPN.
Plus it would boost Notre Dames strength of schedule and they could still work with USC and Boston College or other non-conference teams to add on to their schedule.
Notre Dame wouldn't be playing the likes of Army, Washington State, Nevada, or Tulsa.
Even though Indiana all ready has two teams in the Big Ten in the University of Indiana and Purdue you could still add Notre Dame.
Some of the downsides of this would be you would have to rename the conference or dump a team. I really couldn't see the Big Ten dropping any teams because all of them have been pretty descent. Plus I don't know what you would call the conference with the addition of Notre Dame.
Another downside would be that they loose their current automatic BCS bid if they finish in the top 8 but they have only done that three times in the modern BCS era in 2000, 2005, and 2006. But then Notre Dame would have a shot at the Rose Bowl or a National Championship if they win the conference or go undefeated.
The upside to the bowl games is that the Big Ten has six additional bowl contracts.
Then you would also have to figure if Notre Dame plays USC in the regular season and wins the conference and aren't number one or two they could play USC again in the Roe Bowl.
Overall I don't think this would ever happen but it would be good for Notre Dame and good for college football.
Imagine Notre Dame playing Michigan, Michigan State, Purdue, Ohio State, Penn State, Iowa, and the other teams in the Big Ten each season. It would create one interesting season each year.