An ebike doesn’t pose nearly the risk to the public as a car does, it’s much closer to being as dangerous as a non-powered bicycle, which is not very. If people fall for the argument that ebikes need plates, plates for normal bikes probably aren’t too far off. I don’t think it’s ever going to be the case that overall public safety is meaningfully worse because cops can’t easily track down rogue cyclists as easily as cars, but it’s easy to imagine cops having a real time map of cyclist locations being a threat to civil liberties.

A better way of doing it could be classifying them as motorcycles if they are built to go very far above the maximum speed possible on your own power, incentivizing most that are sold to be slow enough that the safety considerations are more or less equivalent. That would remove any small decrease in safety without building up more surveillance infrastructure.