Some time ago I stumbled across the following:
Despite the objections of purists and the present high cost, it's clear that this is the way of the future. Reviews point out the sophistication of the electronic control; for example, the cages adjust slightly when cross-shifted (an outer gear at the crank and an inner gear at the rear cassette, or vice versa) to eliminate the familiar rattle. The rear derailleur also overshoots so that the chain is driven into the new gear quickly.
Only professional cyclists could have the finesse to do this through delicate control of conventional shift levers, and I know I would be never be capable—certainly not while pounding up the steep hill on Walmer Road, near Casa Loma.
- Bottom bracket dynamos ([hub dynamos](http://en.wikipedia.org/wiki/Hub_dynamo) already exist),
- Wireless tachometry for cycling computers integrated with the above,
- Batteries in wind-shadowed areas (e.g. under the saddle),
- Wireless and/or regenerative braking,
- Turn signals, and
- Cellphones and mobile devices as cycling computers via Bluetooth.
A more modest idea is a crankset side light. Many cranksets (including the FSA Omega on my 2008 Kona Jake) have one arm—on the side opposite the chainrings—clamped around a hollow axle that passes through the bottom bracket. The tube is covered by a small dust cap. Instead of the cap, insert a small device with a dynamo, battery, and a single, blinking LED. This side light would serve the same purpose as spoke-mounted reflectors.
The general concept is that small accessories don't require huge, or any, batteries. By efficiently diverting a fraction of the rider's output, electronic parts can be powered reliably whenever a bicycle is in motion.