Sense, not very common these days
Apologies to the nice man whose quote I stole (damn good one isn't it). The difficulty with all these topics is that legislation has to be for the many and not for the few. As someone said above, the market for these bikes is pretty small and almost certainly does NOT include the cyclists who actually have a clue what they are doing on the roads.
The Public Highways are dangerous enough without adding a new category of 'electric turbo accident seeker' with very small tyre contact area and brakes which need intelligence when applying (hit the front brake first at 30mph and you'll be chewing tarmac before you can say OW).
To all those that proudly (and with good cause) announce they can pedal faster, I bet you know how to use your brakes safely and you still get that pucker moment when some stupid a*** pulls out across you.
As with Segways, the problem with these is not getting it moving but in moving and stopping safely and as such they should be restricted to private land or else go through the full roadworthiness testing that mopeds/scooter have to meet. Not that they would have a hope in hell of meeting it.
I speak as a car driver/motorcyclist who hates bicycles because I'm overweight and unfit and they try to kill me whenever I try to sit on one. If you are going to have two wheels then stick at least a 650cc engine to them.