Sorry Adam, but IMO this is nonsense.
All the energy in this system is initially coming from the APU to charge the battery, so you may as well drive the rotors from the APU and save the battery and electric motor weight.
But it is much worse than that. There are significant energy losses in the electric generator and then the electric motor, so the fuel efficiency overall is much worse than a plain ol' turbine.
When batteries are good enough for a one hour flight, and they are ground charged from a non polluting electric power source such as solar, hydro or nuclear, then it all becomes worthwhile.
As for the Prius - it's a gimmick. You will get better overall efficiency in the *real world* out of a small modern turbo-diesel.