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So if the operation of a nanolight has no restrictions compared to other aircraft, even hang gliders, what's to stop hang glider pilots from attaching a cheapo little electric motor from a balsa model and attaching it anywhere on their hang glider to claim they are flying a nanolight?

You are already flying under FAA exempted ultralight standards.
You don't need a license or a rating.
Airspace is the same, hang glider/ultralight.
Land ownership restrictions of launch and LZs do apply.

Put a motor on it and your glider can weigh 254 lbs.
Without a motor it's 154 lbs.