Well giving it a quick thought here are some idea's for you to consider.
The main thing that I think that will be holding you back is the size of the hub itself. For one it is too small in order to provide an kind of satisfactory torque. Also, the size of the tire creates problems for a driving gear to be placed on the outer ring near the rim.
If you have a very good machine shop I would attempt to build a larger hub that leaves a hollow with about an 8 to 10 inch diameter.
You would have to create a set of two precision rings where some form of a ball or needle bearing could roll between these two rings. The inner ring acting as the sold ring that attatches directly to the forks and the outter ring acting as the hub where the spokes thread into.
With this form of a setup you would have a better combination of tourque and effective gear ratio. Also the 10 inch open space would allow an area to place an electric engine that could be hooked up to the rotating ring to allow for a direct drive from the motor to the hub.
One could also put the battery(s) inside the open hub and this excludes any problems of getting an electric current to transport through any kind of rotating system.
I do believe you could remove the rear drive system of sprockets and gears and replace it with an electrical generator that transports power to the engine located in the hub.
The interesting thing with this is that one could use certain regulators to maintain an optimum pedaling speed regardless of the bicycles velocity.
In my opinion as a life time motocross rider/racer and mechanic this would be your best likely application. As long as you can buld a precision hub/bearing system as mentioned that operates with very low frictino..
Infact it would be even more amazing to create some kind of a magnetically levitating hub bearing, so that the engine IS the bearing and the driving force
now that would be cool.
Hope this gives you some ideas.
