This number is absurdly optimistic. However, if Uber keeps their marketshare long enough to make it to self-driving cars, then they could be worth this. In short, Uber will be your transportation subscription. Car companies would be wise to get a foothold in this space. Then they would have the vertical and could out-compete Uber. If I were leading one of the big three, I would buy Lyft today. The car will become a phone. There are massive inefficiencies in car ownership, and Uber's part in the 'sharing economy' is providing the double whammy of helping cars become less affordable and at the same time, providing the alternative.
The weird thing about Uber is that they have not shown much proof of being able to build anything like a self-driving car. All they have now are promises, smart people and PR - apparently that is enough to get a sky-rocketing valuation. I do agree that transporation as a service is the way of the future. I'd love to just selfdrive-Uber my way around. But I wouldn't be surprised to see car companies leasing vehicles to service providers like Uber. A company like Apple might be more likely to control the entire supply chain because that's what they're good at.