I was thinking of this thread this afternoon and remembered that I saw a Tesla Model S with a Michigan Manufacturer's Plate a few months back.
My guess at that time was the Tesla was owned by Ford and they were doing a competitive benchmark test. I spoke with another person who thought Tesla likely owned the vehicle and they were using a sub-contractor that Ford uses to do some warm weather testing.
If Tesla did own the Model S that was being tested, I'm not sure why it would be running on a Michigan Manufacturer's Plate.