get rid of the drivers and their cars and move to their own self driven vehicles
This is the thing that a lot of people quote as being the thing that will help Uber turn the corner but if anything it'll make turning a profit that much more difficult. As it currently stands Uber is deferring a lot of business costs to drivers. Things like equipment, insurance, fuel, repair, and so on. When they have their own fleet of self driving cars, they take on all of those things that they haven't been paying for. Not only that, depending on the regulation a state/city might have for self driving cars, there might be a very high cost associated with self driving taxis. Yes, Philadelphia is all too happy to jump on, but that's because of the novelty. Years from now when it goes mundane, I'm pretty sure governments will be less affable to companies wanting to have a lot of self driving autos crowding their streets wearing down their roads. Switching over to self driving isn't going to be this panacea that allows them to go crazy insane profitable, there's a lot of costs involved and Uber will have to switch (or pivot since that's the fun word this season) from being just a purely service based company to a more complex company altogether. Pair with that, the ever evolving attitude of governments that will ultimately wane as time marches on, with ever increasing expectations from locals. If they don't have that mental change happen early in the game as they go self driving, they won't last long. I've seen tons of companies try automation and them not fully understanding what they're getting into is a killer (worst case)/hindrance (best case) for most of them.
I'll add this, what Uber wants to do is of a scale that I've never dealt with personally, so something this large might have totally different challenges and I'm just talking out my butt. So that said, take all the above with grains of salt. But I do think that those are rationale challenges that they're going to run into down the road which will prevent them from being insta-profitable the second a robot hits the street.