I think Crystal is only allowing bikes on 2 miles or so of their network.
In the U.P.: Marquette - NTN Network is grooming a number of miles of their South Trails for snowbiking. Michigan Tech is allowing snowbiking on certain trails, Swedetown in Calumet has Fat Tuesdays with biking allowed in the evenings...
I know this isn't Michigan but stokely creek resort allowed them last year. They are located outside Sault Ontario. Huge amount of trails to ride there.