I think some sort of joystick would be a great solution. Maybe over 15mph it gets disabled and autopilot takes over to take you to your destination (i.e. Walmart parking lot) and then when it slows down the joystick can be used to direct the car to where you want to park.
I can see a joystick becoming dangerous at high speeds though, which is maybe why they have stuck to steering wheels.
Joysticks don't take much to accidentally push forward or ya k back on, suddenly speeding up or stopping your vehicle, or if a kid or a pet starts misbehaving and knocks it to the side.