Isn't the more natural play for uber to position themselves in the market for enabling early purchasers of self-driving cars to offset the cost by having their car go out and be a taxi when they're not driving it?

Uber got where they are - managing a massive fleet of vehicles - not by purchasing cars, but by getting other people to purchase cars on the assumption that uber would help them turn that investment into an income stream. Self driving cars raise the prospect of me being able to turn my car into an income stream without me even having to go out and drive it.

If uber do it right, people will buy fleets of self-driving teslas just so they can rent them out via uber, and uber won't have to invest a penny in depreciating vehicle hardware.