How much power do you suppose yer motor of choice could handle before breaking?
....Probably around 1,000 watts. It wouldn't break but the winding might burn up. The model airplane guys often get 1,000 watts out of the motors for a short time (few minutes) (of course they have more cooling air that we do).
One problem for a bike though is the gear box. It would have to be huge. Higher rations to start out with and much bigger gears. My gear box is extremely light (several ounces) because I am only delivering 100 watts. Even if I wanted to double the power I would have to go to a bigger gear box.
What happens when your looking for higher power is the system grows in weight by a lot. Higher weight means the battery has to be much bigger adding even more weight. From 5 pounds it can quickly grow to 15 pounds.
Accelerating 15 extra pounds take a lot more power.
One last thing. Trying to start from a stop is very tough to do. My system is limited to no lower than 2 mph. Gearing is chosen to get he optimum range of assistance. Many commercial assists are also limited by the same gearing set ups.
So if your only looking for low end help and limited speed you can do it mainly with a high ratio gear box. The motor is easy.
I use my system for acceleration a lot. to help me get up to cruising speed.
D: I had hoped to use the supercapacitors in lieu of more batteries. They might hold up for a few seconds.
Yeah, the gearbox seems unavoidable.
I wonder if any motors have a high-torque design in mind.
Maybe model airplane motors aren't the best place to start.