Looking for ideas on how to track bike wheel rotations or distance traveled
Two main technologies picking bicycle speed are magnetic sensors and pickups counting wheel revolutions and ANT+/Bluetooth sensors with accelerometers  counting wheel revolutions. 

Magnetic sensor into a micro controller would be trivial and is not really a bicycle question. ANT+ sensors follow a standardized API so you could look for a micro that support ANT+ and look at the ANT+ API for bicycle sensors. 

Not sure how the accelerometers go on stationary bikes as they auto calibrate distance/revolutions, and a stationary bike has 0 distance.

I will ignore GPS...