I understand your point: Michigan v. Ohio State is the most important B1G game, and so it needs to be played the last day of the conference schedule. And, you say, the game would lose importance if Michigan and Ohio State were then to meet for the championship the following week.
I am not sure that I agree. First, it is quite likely that the Michigan-Ohio State game would determine who gets into the championship game (suppose Michigan needs a win to get past Penn State) , or who would have the home field advantage in the conference final. Second, there are all kinds of traditional rivalries that used to be on the last Saturday of the season that have since been moved without harm. For instance, it used to be that the last Saturday of the season in what was the Pac-10 would have Washington v. Washington State, Oregon v. Oregon State, Cal v. Stanford (the "Big Game"), USC v. UCLA, and Arizona v. Arizona State. Those games are no longer on the last Saturday, and yet they remain important rivalries. Third, at present the B1G championship game is a joke, with Michigan or Ohio State playing a far inferior team from the other division. Maybe it's worth sacrificing tradition so that the championship game can become a real focal point of the season, rather than another blowout.