I'll jump in here as well:
A: We still only use about half the cycle to produce power. In the 12-6 o'clock position we have nil torque arm if we assume that we have very poor power in the forward-on-top and rearward-at-bottom parts of the stroke. This still equates to erratic torque.
And the 12-6 positions are also addressed with the powercranks in my opinion. If you don't push forward and pull backward in the stroke, your pedal will simply stop.
B. We have the issue of aerobic limitations. I.e. the cardiovascular system can not support an increase in power over any lenght of time even if we have the muscles to do it.
This certainly is not true in my case, I don't know about others. The limiting factor for me is not oxygen uptake or cardiovascular system but the build up of lactic acid locally in the muscles. By distributing the load on more muscle mass (pulling up, back and forward) I decrease this limiting factor and I can get a little closer to the limit of the central systems for oxygen uptake and distribution.
About the spring storing idea: Wouldn't it be better if we could store the energy from several full revolutions of the cranks? That would make a better job of producing an even torque curve.
Just one catch: If memory serves me correctly the ICU rules states that no form of energy storing mechanism is allowed. That would include the cranks we are talking about. Feel free to correct me if I'm wrong.
Regards Göran