markrj wrote: It's very simple stepper motor technology.
Bicycle gear shifting is not rocket science.
No, it's a servo not a stepper motor. Stepper motors are constructed so that input pulses turn the motor coil by a known amount, whereas servos can run on bog standard DC motors, connected to a potentiometer which measures the position reached by the output arm and feeds back the position to the control electronics.
There are servos and servos though... ...the best ones run on DC coreless motors using digital power electronics to avoid any positioning errors. These are the sort of servos which cost £100 and are used to allow model helicopters to fly backwards at 50mph doing aerobatics with the tail locked in position. Likely a bike derailleur servo would have more in common with the helicopter swashplate servos which trade off a little bit of speed for a lot of torque. I would be surprised if you couldn't find a standard RC servo motor and electronics combination able to cover bike applications as they make literally hundreds of different sizes and types. Of course then you need to think about integrating it into the derailleur, waterproofing, driving it... which all makes it very non-standard, but the servo mechanics and electronics should be off-the-shelf.
But I will agree that the technology is not new and in principle shouldn't cost £££s.