Well okay. If you really feel that being able to take a trip to a less accessible location at a few seconds notice at peak times is vitally important to you, then you're still free to own your own self-driving car.
But I think most people would much rather wait a few minutes on those occasions and save their money.
(And FWIW, I think it could be fairly quick, since you don't have to pay a self-driving car to sit around in a small town in case someone needs it.)
No.
You will have to call the taxi and wait for it to arrive, and (inevitably) you're going to have to wait a lot longer at peak times.
That is not the same as going any time you want.