I think the bigger spook will be if the entire market for on-demand drivers suffers a big decline in demand. Izabella Kaminska of the Financial Times has writte

I think the bigger spook will be if the entire market for on-demand drivers suffers a big decline in demand. Izabella Kaminska of the Financial Times has written several articles arguing that the Uber / Lyft model is fundamentally uneconomic. Without arguing for or against her, if that turns out to be true you are going to terrify a large number of investors. Nothing else has really looked as much like a sure-thing disruption opportunity as the taxi market. Anecdotally, my most recent Lyft driver recently told me that Lyft has started playing a lot of the same games to shaft drivers that she left Uber to get away from. It does make me start to wonder if the entire thing is largely subsidized by a market flooded with cheap money.