You're right that there are probably a limited number of teams doing the home and home thing, but we know there are teams willing to do it. MSU just announced future games against Alabama and West Virginia. OSU has Mia (fl) and Cal in the future. It isn't that hard to do. You just do it. With the 'new' Michigan Stadium, though, I don't see anything happening that will take games away from Ann Arbor. If M ever returns to the Top 10, there will be a lot of criticism regarding strength of schedule, and it will likely be justified.
After M beats Delaware St. this year, we should never have an I-AA team in Michigan Stadium. (we have to play them this year, so our record is 1-1).