I'm going out on a limb here and boldly asserting the power assist is superfluous to the turn signal and brake lights. Though I've no evidence to back up this wild assertion, I'll claim one could fabricate such a contraption for under $10.
Oh, wait, sorry, yes I do:
http://www.youtube.com/watch?v=vqz4PzAXzd8
This one's pretty cool:
http://blog.makezine.com/archive/2009/03/diy-bike-signals-with-accelerometer.html
There are thousands, if not tens of thousands of DIY plans for this sort of device out there.
No, I haven't one myself, yet. In the lull between morel season and the Green Quilts, I think I'll fab one.
I'm solidly in agreement that "Visible, safely, predictable, and courteously" is a splendid mantra, but, save for "safely", it dances around the real issue: communication.
If more then a few wheelpeople in Pgh had LED matrices fore and aft, which could function as not only brake lights and directional indicators but also as messaging devices, the attitude of Pgh drivers would change more quickly then it would otherwise. Though I believe this, I (really) have no evidence to support it. However, it is a testable hypothesis.
The messages could be programmed, and controllable by a simple switching device. Heck, one could likely interface some portable computing doohickey like an iPhone. Messages could include, (but obviously are not limited to), "Thank You", "Pardon Me, But I'm Taking This Lane", "Please Back Off, You're Scaring Me", "Hey, I'm Here", "Kiss Your Mother With That Mouth?", and the immortal classic "F*CK YOU MOTHERF*CKER, JUST TOOK A PICTURE OF YOU AND DOWNLOADED IT TO THE POLICE!"
Call me crazy, but I think holding a mirror before an as*hole is the best way to get them to face their behaviour. Barring that: public shame and humiliation. Pillory Rules!
And, though the notion triggers an involuntarily shudder, with such a message board one could attract sponsors...
Ride fearlessly. (Brought to you by...)