They're already not the only ones, there's cabify, mytaxy and a few others.

The drivers gladly use multiple apps so these businesses don't really hold much power in terms of lock-in.

I can imagine it. I’ve lived in San Francisco since 2011, and I remember using Uber, Lyft, and Sidecar. I have had long periods where I was “loyal” to each of those three, with Lyft being the current and longest-lived loyalty. At various times in the past I would comparison shop between all three, looking for the cheapest or quickest option.

So you’ve witnessed zero new successful entrants in 7 years despite a huge market.

On the contrary, Lyft and Sidecar both launched after I moved to SF, and I believe Uber was only a black car service when I moved there.

Setting up an airline isn't cheap either but plenty of people do it.

Setting up an airline is easier. You can lease a plane or two and fly one cherry-picked route. There’s no chicken/egg hurdle.

Buy a bunch of self driving cars and deploy in a city. No chicken egg there either.

Except self driving cars don’t exist.

Yes it would be fairly easy:

1. Start in one city only and concentrate on that. 2. Get your service listed in Google Maps. 3. Gradually expand.

Job done. The only real defence against that is that Uber/Lyft could probably afford to undercut you until you go out of business, Walmart-style.

Can you point to an example of anyone doing this (successfully)?

Yes there are actually loads of regional Uber-like companies that only operate in particular regions. Most recently I went to Thailand where they use Grab. It is advertised in Google Maps.

Do you think Waymo will build its own network or hitchhike onto someone else’s? If they choose the former, I can see them being a contender.