analogy to weapons?
I wonder if this would help? A few years ago "airsoft" or plastic BB handguns, rifles and even machine guns started to become popular, which were so realistic that they were indistinguishable from the real thing.
The response was to legislate that those sold over the counter had to have 50% of their material made of fluorescent material, so that they could be seen as "toys". Other ones could be kept fully realistic, but they could only be bought if the purchaser could prove he belonged to a gun or skirmish club.
Would it be possible to legislate so that multi-rotors capable of carrying an external camera or FPV equipment could only be sold on production of proof of model club membership?