One possible path is the hybrid aircraft, where combustion turbines or fuel cells produce electric power that drives small ducted fans via electric motors. The enabling technology here is superconductors. Airbus is working on superconducting motors and generators for such hydrogen-powered aircraft.
One can imagine regenerative braking in the fans, for example to recover energy as aircraft descend, and also with batteries providing emergency backup power.
One can imagine regenerative braking in the fans, for example to recover energy as aircraft descend, and also with batteries providing emergency backup power.