Earlier quoted context omitted.
That's actually a really interesting question. Because it's not necessarily about handling most usage, but also about handling peak usage. Is it worth the cost to keep everything 4-seater if that means they can all enter "carpool mode" whenever required at times of peak demand? Because once they become ubiquitous, I suspect the vast majority will be operating in carpool mode at rush hour. Most people won't be willing…
My impression is that the shared ride options on Lyft/Uber only give a small discount and see little usage. Sharing rides is only more difficult and less attractive for Waymo users, who won't have a third party to buffer interactions.
Of course it's less attractive at the same price, but if it's cheaper enough it becomes more attractive for the average rider. And we can even imagine cities implementing single rider surcharges at rush hour to keep traffic running smoothly.
Rush hour will be a bottleneck. So something has to be done, and it will involve trading off price and convenience. Whether it's carpool mode or self-driving buses or likely a combination of the two.