There is what some people say is a gray zone (I don't actually think it's that gray) where a device is too fast or powerful to be a legal e-bike, but also doesn't meet the requirements to be a road legal motorcycle. Will Progressive give me motorcycle insurance on my DIY e-bike without a VIN? Will the DVM register it? I don't think so. In most states there is no path to legality, at least as far as operating the thing on public streets goes.
I don't think that's necessarily a problem that needs solved. I'm fine telling the person that bought a Sur-Ron, "too bad, off road only".