I believe that this law is in direct violation of the commerce clause[1]. The commerce clause was designed to prevent tarrifs from being placed on products from one state being sold in another state. They wanted to prevent inter-state trade wars. Being forced to go thru a dealer network that (theoretically) adds no value while extracting a cut of sales is a form of a tarrif (or at least, I think it is arguably one).…
Michigan is not discriminating against Tesla. They are not saying "only Tesla may not sell direct to consumer." Instead, they are saying "No auto manufacturer, regardless of their state, may sell direct to consumer." Thus, no commerce clause violation.
I think they took the safest approach