1. Engineering - Have they created a "breakthrough" technology (10x better than current tech)? No.
2. Timing - Is now the right time? Maybe they're gambling that self-driving cars are only a few years away so they can subsidise human drivers until that happens in order to build a brand and demand/market presence.
3. Monopoly - Are they starting with a big share of a small market? Only by subsidising prices which isn't sustainable.
4. People - Do they have the right team? Not sure.
5. Distribution - Their app has widespread distribution and some key partnerships solidify that.
6. Durability - Will the market position be defensible 10 and 20 years in the future? I can't see why it would be. If they're betting the company on self driving cars, then that removes any benefit of a network effect based on a two-sided market. Fast forward 10 years and another well-funded company could pump a city with autonomous cars which would face little barriers to entry (barring regulation, but they'd probably ignore it like Uber have).
7. Secret - Have they identified a unique opportunity that others don't see? Not unless they can move into adjacent markets or have a major ace up their sleeves, but there are so many competitors that it would seem they haven't.
They are obviously targetting economies of scale which would mean their plan is to keep prices so low no one else can afford to enter the market barring major technological innovation. This must be why they're burning so much cash.
Self driving cars would remove one barrier to entry since once they exist there will be no need to have a pool of human drivers. So in that case there would be no network effect to act as a barrier, only any effects of economies of scale. That means there's potentially no monopoly being fought over, and therefore no monopoly rents to be gained. Economies of scale take funding to break into, but probably won't inherently create a monopoly with a significant defensible position a well-funded competitor couldn't break into.
Is their valuation the result of a bubble because investors have few other places to put their money? Google invested, probably just hedging their bets or buying access to a future market, and now their valuation keeps spiralling...