If one put some smallish batteries in the system to deal with transient power demands, I could see a 1000W genset driving a pair of 600-700W hubmotors. Only on hard acceleration and hillclimbing do you use all the output of the motor- most of the time, on more level ground, only a fraction of the motor's output is used. Batteries of about 14AH in parallel with the motor speed control output could cope with sourcing the 400-500W the gennie can't supply, in the short term. When the load reduces, the genset returns to charging the batts.
One would have to be a bit clever in connecting the speed controller and batts to the motors. The batt charger used would also have to be fairly grunty as it would see the load of the motor on high demand, though would be sharing it with the batts and the spd ctrl.
It'd be a bit more practical if the genset were wound suiting the motor voltage i.e. 36-48v so it could be connected straight to the batts without a charger (perhaps some current limiter ckt would be needed), but the little Hondas usually are wound so their main output is 120/240v but some also have a second, low-current, 12V batt charging winding.
Mains AC batt chargers usually only deliver a few amps, not the 30-40 an ebike may need on hard acceleration. If one plugged a mains voltage charger into a genset, not much of the gennie's output capacity would be used.
