I disagree with the idea that self-driving cars will have the same commodity issue as today's car ride services. How could a significant decrease in operating expenses not increase the profit margin?
Let's put it this way - if you had the choice between paying 1/5th of what you pay now for the cheapest ride available, or half what you pay now for a ride in a nicer, cleaner car that picks you up within seconds, which would you pick? My guess is that with those choices, more people won't pick the cheapest option available.
You will find yourself hard pressed to find a company, which is the first to bring something market and being in the dominant market position.
Self driving cars will be a commodity. Whatever advantage it gives, any company will have it, so there is no way it will increase the margin.