Where are well-funded new entrant going to get self-driving cars from? Uber/Google don't have to sell self-driving cars to the public, and by the time self-driving cars happen, Uber's already got an app and the infrastructure to run the app, as well as the engineering expertise in running that infrastructure. In addition, they already have the installed base of customers that default to the Uber app for their transportation needs. Self-driving cars aren't going to take over instantly, either, so there will be a slow transition period of phasing out manual-drivers.

Whether Uber's billions in losses can be amortized over that time so those losses aren't on the books so they can be competitive with a new entrant solely using self-driving cars, remains to be seen.