Hmm I wouldn't say that these are "gaining popularity" unless that means going from 0% of people to 1% of people.
99% of people will just buy from one of the big three. Some people will buy some cheap foreign bike off of Amazon, etc., unaware that it is illegal.
Also, this is not about Bafang bikes in general, but cheap Chinese ebikes in general. Also, I have no idea why, but this has apparently been a problem mainly in Osaka. (I have noted this on the news a few times, and it's always in Osaka. The police will see someone going up a hill without pedaling, etc. - Dead giveaway).
What is really interesting is this:
1. Street legal PAS bikes have the limitation of 24kph, no throttle, etc., and can be ridden backwards down one way roads, on the sidewalk (as an exception), bike lanes, etc.
2. Higher powered eBikes have existed, but are always required to be registered as a moped or motorcycle.
There seems to be some mixed information above...
There is *already* a law that says that *anything* with a motor is classified as a motor vehicle, which requires license, insurance, registration, helmet, license place, mirrors, brake lights, etc., etc. There is also a very specific exception for "power assisted bicycles", which means anything that can only go up to 24kph with a maximum of twice the rider's power input at 10kph and 0 at 24kph.
The situation under the current law is, simply put, the imported bikes that don't comply with the existing PAS regulations will be treated as motorcycles by the police when found, and if they don't qualify as road legal motorcycles/mopeds (or Gentsuki), you will be in trouble. There is no need for any new law about that at all - the existing law is clear.
The only real thing that is needed is to have Amazon and the other online retailers involved put a big disclaimer that says "THESE ARE NOT ROAD LEGAL. FOR USE ON PRIVATE PROPERTY ONLY or you MAY BE ARRESTED AND JAILED", so that people can't play stupid when they do get caught.
But the license plate cover thing... that is interesting.
Until now, there was no legal way to "switch modes". For example, the battery on my "moped" ran down and I had to pedal it home under 100% my own power once. Technically that's not legal. Likewise if the motor broke down and I had to pedal it, that would be "operating a malfunctioning motor vehicle". Realistically no cop is going to stop me for that since it just looks very much like a normal bike, but still. Also technically I can't ride that bike on the sidewalk or bike lanes even when the power is turned off, because it is registered as a moped. If I took off the license place, I could 99% get away with it, but technically that's not legal either. If I kept the license plate on, then it would be obvious I shouldn't be riding on the sidewalk. If the "cover the license plate" option is available and somehow links to the power output, that would be very nice indeed.
I have imagined a system before where there would be one bike with two different head units that would allow you to switch it between PAS and Moped mode in a way that would not be easy to play funny stuff with the cops.
And for the record, most people in Japan don't purposely break the law. It's not worth it to be arrested for something silly, but it's also just frowned upon in general. You would probably be fired the moment you were arrested, shunned by your family, etc.
Usually for bicycle offenses like accidentally running a read light or not running with your lights, the cops will just give you a warning (speaking from experience!). For operating something that does not qualify as a bicycle without a license, registration, or insurance, though, I am quite sure you would be looking at a 10 day detention plus fine/jail time - at least if they thought you did it on purpose.
Japan is far from a surveillance state, but prosecutors don't usually prosecute "iffy" crimes either, as a failed prosecution looks really bas on the prosecutor's record.
"Bicycles already have to obey the same traffic laws as registered vehicles have to obey." - Yes and no, something classified as a bicycle can go the "wrong way" down one way streets legally in most cases, can ride on the side walk most cases as an "exception" (i.e. you should try to avoid doing it as much as you can if you feel safe), can use bike lanes, bike trails, etc. There are extra requirements for making a two step right turn. On the other hand, running red lights, etc., is still illegal, but usually treated much less harshly.
btw, I have seen tear downs of Bafang motors. Really really bad build quality with solder gobs everywhere, etc. You do get what you pay for.
At least the worst a cheap motor can do is break, I am much more worried about cheep batteries that can explode, etc.
btw #2, the same issues have been caused by "e scooters" recently as well, as some people were riding them around without realizing they needed to have a license plate and all of that jazz. (They don't qualify as PAS bikes...)