I think e-bikes are going to have the same issue that scooters and mopeds have (and even bikes too) - safety. If you live in a city, you are going to have to be riding near cars, and it is simply a fact that a collision is much worse when you are on a bike or scooter than when you are in a car. A minor fender bender in a car could be serious injury on a bike or scooter.

Everyone I know who commutes to work on a bike has been in an injury accident, ranging from bad cuts and bruises to broken bones and brain injuries. When you combine the basic lack of courtesy from car drivers, the inability to see bikes compared to cars, and the exposed nature of a bike rider compared to a car, the danger is simply too great for many people (myself included) to take.

Unless we get lots of dedicated bike roads where you never have to interact with cars, I don't see how this problem is solvable. As ebikes get faster and more powerful, the danger is going to increase rather than decrease. This is the same reason I don't ride a motorcycle; while it would be efficient and quicker to commute on one, they are simply too dangerous.