This was interesting to see. Its similar to what a few mfgs are doing by fully powering up the alternator during braking, but they're using capacitors to be able to capture more energy. They're also bumping up the alternator output voltage to capture more energy as well (variable from 12-25V). They claim a max FE increase of 10% which is what we've seen be eliminating the alternator here on EM.
Mazda Improves Fuel-Saving Start-Stop System With Capacitors