For low powered electric bicycles these changes would be a solution without a problem.
I'm sure the real problem that is trying to be tackled, is that it is difficult for authorities to catch, fine and confiscate the more extreme powered bicycle uses with the current regulations, short of towing around a mobile dyno (oh I hope I haven't given them ideas...).
So what do they do? They clarify the rules with the pedal first thing and speed limit which without some pretty clever engineering would rule out all the 2 stroke petrol engine riders, and the unridable scooter style bikes in one fell swoop, much easier for police to pull people over and check for this type of compliance. And no costly and annoying court challenges.
But you know how it would go, once the police have a heads up about powered bikes we would all get picked up sooner or later. And I recon because this is not a compliance plate/design rule issue the rule would just be retrospective, with no quarter given for those who have existing bikes.
Personally I don't want get 50watts and lose the flexibility and safety of a hand throttle and reasonable top speed. From the discussion paper I've read we haven't got buckleys of getting significant increased power.
Maybe we need to suggest a viable alternative method for policing the 2 stroke and overpowered types (Yes I know there are lots of over powered riders here , but you already know you naughty boys, without me or the police telling you
What about putting it back to the importers and retailers, with some kind of code of conduct or compliance.