It turns out they already passed something like this in MN:

Subd. 90. Electric personal assistive mobility device.
"Electric personal assistive mobility device" means a
self-balancing device with two nontandem wheels, designed to
transport not more than one person, and operated by an electric
propulsion system that limits the maximum speed of the device to
15 miles per hour.

I had thought that Segways were faster than that, but after looking through segway.com, it looks like they're only up to 12.5 mph. I can tow a trailer behind a bicycle a lot faster than that. I guess I'll have to play nice (but they sure do take up a lot of space, almost as much as a rollerblader and they're even slower...)