There's an MIT spinoff called Top Flight that was working on a hybrid quadcopter, IIRC. I think the main reason you don't see them in the hobbyist space is size

There's an MIT spinoff called Top Flight that was working on a hybrid quadcopter, IIRC. I think the main reason you don't see them in the hobbyist space is size floor (you need a pretty big machine to make the weight overhead of the motor, generator, and charge circuitry work out) and money.