What kind of innovation are you expecting? Plenty of innovation is still happening in the realm of adding motors and batteries to bikes. Beyond that, what else is there to do with bikes? We're already deep into the realm of severely diminishing returns on weight and aerodynamics, and braking power is limited by physics. What else is there to improve? All I can think of is ABS.
Has anyone looked into a pneumatic powered bicycle? Is it way less efficient than a chain drive? What if you pedaled to compress air into a reserve tank that was then discharged to somehow propel the wheel(s)? That could soften the peaks and valleys of power and allow perhaps for regeneration during braking. With a large enough tank you could save up power during plains to propel you up large hills.
I'd think that a pneumatic bottle would have to be very large, and/or very heavy to store enough energy for a useful return, the heat lost from the compressed air would lower efficiency, and an air turbine that can provide usable power over a wide range of pressures from the bottle would add additional weight and contribute to inefficiency.
The fact that there are few compressed air hybrids is probably a good sign that it's not significantly better than batteries.
Few electric bikes even use regenerative braking, it's generally not worth the weight and complexity.
