What's actually changed here? Petrol engines on bicycles have long been allowed so long as they don't exceed the equivalent of 200W power, with anything more powerful requiring registration.

Source: this info sheet from 2016 https://www.transport.tas.gov.au/__data/assets/pdf_file/0015/141117/Power-assisted_pedal_cycles_-_Information_Sheet_-_Dec_2016.pdf

A lawnmower engine on a bicycle is already outlawed. If they're now cracking down on tiny engines, that doesn't seem to be supported by the "high speed" description.

I have no particular love for these noisy bicycles but the legal ones are harmless enough.