This is cool. Acts like a supercharger until the turbo kicks on.
Is a supercharger rather than acts like a supercharger.
Not an entirely new idea, though this might be a better implementation than previous ones.
Idea discussed/predicted here, from about halfway down. Most of the links are dead though, since the thread is almost 10 years old. They don't make threads like that anymore.
The turbo's power is the key. They mention 5kW which converts to 6.7 hp at the turbo. That's the type of power you need to compress the volume flow of air a car engine uses. The other thing is duty cycle. Like a starter motor, the electric motor for the turbo is probably operating in deep overload, so it can only operate briefly without burning out. It's an interesting concept.