> Will waymo even be available in less mainstream areas?

Ever is a long time. It's not reasonable to predict beyond a decade or so. It's easily possible that this becomes huge and in the 2040s people are astonished that "driving yourself" was a thing, the same way it's hard to comprehend now that most people weren't literate. Not "Couldn't write an essay / read a newspaper" but "Couldn't sign their name / read a postal address"

But it's also possible that this goes nowhere, and outside of a few large cities there is never a robot taxi market, it just doesn't exist. Waymo is, among other things, a bet that there is a large market.

Dense places are where it starts, but that was also true for the telephone. Bell didn't provide service to tiny rural settlements, they wired places like Boston and New York, AIUI the general service provision was a government initiative even in the US, it was never strictly profitable enough for huge corporations to spend their own money making it universal.