These contraptions are illegal to use in public and if they become popular the laws against them will be enforced immediately, because they're incredibly dangerous.
It is impossible to provide effective braking on a skateboard. The rider has absolutely no means of impeding their forward movement, so even if the board has effective brakes it's just going to throw them off. This is a minor problem if you're rolling around a skatepark, but it's a Big Fucking Deal if you're commuting in traffic.
It might be conceivable to overlook this failing if it weren't for the fact that tiny unsuspended wheels have almost no capacity to absorb bumps and road defects. Anyone who skated as a teenager will remember being thrown to the ground by a small piece of gravel stopping the wheel.
Add 2000w of tractive power and city traffic and you've got a recipe for disaster. Someone is going to die, their family will sue and they will quite rightly win enough money to bankrupt a small company. Boosted Boards are marketing their device as a vehicle and advertising it's suitability as a means of transport, which completely obliterates any defence they might have had. The laws against unlicensed motor vehicles will be enforced and the police will start confiscating them on sight. The electric skateboard returns to it's rightful place in the gimmick section of a sporting goods store, next to the mini-scooters and the moon shoes.
The bicycle has been a safe, practical and sustainable means of transport for over a century. Modern bicycles are lightweight, efficient and have excellent ride quality and braking. Short-range urban transport is a solved problem in all but marketing - Americans remain inexplicably certain that cycling is not for them.