250w is also fine for me.
Regard the comments in the article about cargo/family bikes - these are all issues that are solved with better gearing not larger motors. I recently transported bricks (in a trailer) using my bike, I reckon I was hauling 60-80kg. A crawler gear was definately needed when setting off or up 1 hill but otherwise when moving I was using the same settings as I do normally, momentum was more helpful than a larger motor.
The comments about how it would affect the consideration of an ebike as "just a bike" is the important bit to me
Thats exactly my main concern. Any change to e-bike that forces me into registration, insurance etc will instantly turn me away from e-bikes. This is nothing to do with unwillingness to register, get insurance (I already have 3rd party liability) etc but the police's lack of action towards dealing with the current abundance of illegal electric motorbikes. It gives me no motivation to comply with such a law should it come into force so I'll simply go back to a bike that doesn't need to comply.