Any taxi service will rely on several elements which limit their service area:
1. Availability. How many vehicles are in an area, that can respond to dispatch?
2. Demand. Can't have too many idle vehicles scooting around and taking up space.
3. Service. Must establish depots where the vehicles can return for charging, cleaning and maintenance.
4. Support. Waymo Support is a tap away, and if a vehicle gets particularly jammed up, they will dispatch a technician in their own vehicle. Support can also monitor telemetry and push commands to give nudges (but cannot remotely drive a car).
So with the current model, I do not envision Waymo service areas expanding beyond the reach of their depots, or offering long-haul trips between urban centers.
They scaled from 10k to 100k per week in a year.
They've been operating successfully on highways for months now.
Once they can do highways, a huge fraction of the US will open up. And generally speaking, driving outside of cities is quite a bit more easy.
They seem like they're moving very quicky to massive deployment. Comma is still just driver assist.
Custom vehicles that can strip out all the complexity of a steering wheel will reduce costs pretty aggressively.