Can you buy or put together a crank set with sprockets on both sides, so you could keep all the gearing and engage on the left side? That way it would be easier to carry a set of cranks that could easily bolt on if you ran short on juice. Plus the low gearing on a full suspension mtb could be kinda fun. I'm interested to see what you come up with.
Can the batteries take the charge as fast as regeneration would supply it?
I've been toying with the idea of a small honda 4 stroke with a centrifugal clutch like I have on my vespa on the left keeping the gearing on the right, but electric sounds interesting. Especially as an aid to pedaling a street bike for higher speeds.