Uber is losing billions and their drivers are making peanuts. That sounds sustainable.
They are basically biding their time until driverless cars take off it seems.
Let's assume, for the sake of argument, that the concept is viable in urban areas within 5 years and Uber puts a massive fleet of self driving vehicles on the road.
While it's certainly true that they wouldn't have to pay drivers it would be a massive shift in capital investment.
The "genius" of Uber is shifting the necessary capital investment for hundreds of thousands of vehicles onto the drivers.
Assuming one car costs 30K (which I think is on the very low side) it costs 3Billion to put 100'000 cars (which also seems very low with Uber's global ambition) on the road.
That's an upfront investment currently incurred by the drivers.