The (buzzword warning) hyper-growth startup model is in essence 2X revenue, 1.5X costs. Repeat until inevitably profitable - and I say inevitably because with enough time, 2X revenue, 1.5X costs gets to profitable. The only variable there is having a long enough runway.
Uber seem, from the financial data I have seen, to be sticking to that playbook down to the 3rd decimal place (exaggeration for effect). When Uber does turn the profitability corner, it will be at a level well over a billion a quarter.
Sure it's a risk, but if any company was setup to be huge, had followed almost all the meta-rules on growth and looked to be hitting those growth targets, it is certainly Uber.