That is a great concept. Think about how much money Caltrain could have saved if they didn't have to put up catenary the whole way from San Jose to San Francisco. Not having to maintain the catenary and do periodic replacement of the wires (other than in the station zones) will also be a big cost savings. With the big strides in battery technology something like this was expected. Where this concept shines is having the train pull power from the catenary while under acceleration. That's huge. Most of the energy used is all in acceleration. Regenerative braking can push a charge back into the battery so no energy is wasted.
Very cool.