Yeah - I can understand how so little time is invested in braking - yet my point is that the system would utilize "both" energy sources and give a rider a chance to manually "put up with" charging the system when he chooses. Or if necessary - go ahead and plug in the battery at the end of a ride.
I think the technology exists - whether it is marketable or can be made attractive - I don't know.
I do know, that if you ran current hub generators every time you "coasted" downhill you could keep a battery charged. And leave these generators off during hill climbing or most of the flat part of a route. (OK maybe not in the desert)