How about forgetting the whole "e" part of this, and just accept that a motor is a motor, whether powered by a battery, gas, diesel, moonbeams or whatever.
The question then becomes: at what power level should it require regulation?
We don't differentiate between a gas powered car, hybrid or all electric, so far as licencing and rules of the road are concerned, why should we make any distinction for two-wheelers?
When my step-dad was a kid in Holland, he had a little 10cc gas motor mounted to the front forks of his bicycle, it would push him along on flat surfaces at about a normal, casual riding speed, but he would still have to pedal to go uphill.
I don't have a problem with people riding something like that without any regulation beyond what's needed for a human powered bicycle. Similarly, I think disabled people should be able to have powered mobility devices that let them move along at the same pace as normal walking traffic.
But as soon as you get higher powered - certainly 30+ kph is well above that - I think it is perfectly justified to start considering ANYTHING motor-powered to be a motor vehicle. That includes e-bikes, scooters for the disabled (the ones that I see passing bicycles in the bike lanes), pit bikes, rainbow-powered magic ricshaws... anything.
Maybe total power in torque at the wheel, or power to weight ratio, or something like that should be the measure, and it certainly would be sensible to have multiple classes, with different insurance and licencing needs.
We already have different vehicle classes, licences and insurance requirements on the 'big' end of the scale - cars, trucks, A-Z transport, multi-trailer transport, busses, etc. Seems to me is that all we need is a few more categories on the 'small' end.