They left it open to challenge in the middle. Basically, anything more radical than the U of M undergrad policy is void. Anything less radical than the U of M grad policy is acceptable. Anything in the middle is actually in the void.
It would be interesting to see a policy that fits between these two being taken to the court and hammered out. But logically speaking, these are just two outside boundary posts now, and not much else more, until we read the majority opinions. When they are available, somebody please link them.