An interesting thought. How small can self-driving vehicles be? Would you ride a self-driving motorcycle? A self-driving wheelchair? How about a self-driving Segway? You get on, hold on, and it does the rest. The technology for getting this working at all (let alone safely) is a long way away, but perhaps it could happen.

Without the exercise capability.

You could remove the seats and install an exercise bike.

that's a terrible analogy :) ! more like a taxi without having to speak to the driver or a personal bus.

If only my bike powers and steers itself