Yes it will indeed be a breakthrough if he managed to generate electricity out of gravity and nothing else. Perpetual motion is not possible under earthly conditions with factors contributing to the loss of momentum even when a generator is not connected to the load. May be if someone could find a way to eliminate friction completely, then may be a turbine that can keep rotating is possible. However connecting a turbine to a generator is like applying brakes.

So good luck is all i can say. Let's see when he will be done with his 10% remaining work. Perhaps it will be revealed to him that perpetual motion is not possible when he is done with 99.9% of the work, but that remaining 0.1% keeps things from happening. But by all means I would be happy to be wrong in this case.