Why would driverless cars be smaller? They still need to be able to carry the same number of passengers; the only difference there is that one of those passengers is no longer also a driver.
With autonomous cars, robotaxis become feasible. If you're buying a car for yourself, you're going to want a certain amount of space for passengers or cargo in case you need to do something like drive your family to the airport. You'll also want long range in case you decide to go on a road trip. Even if 90% of the time you'll be commuting alone 20 minutes to work, you'll want this extra range and capacity for the times you need it.
If you're deploying a fleet of robotaxis, most of your fleet can be vehicles that only carry one or two passengers at a time on short trips. If a family wants a ride to the airport, then they'll specify that they need a larger vehicle for more passengers and luggage, etc. So you can buy a fleet of mostly smaller cars with a shorter range, and compliment them with a few minivans for long range trips. Overall your fleet will be quite efficient.
Yep, and given that some big percentage of car seats are not properly installed, do you then have to take the requisite minutes to install and uninstall each seat properly? There are a lot of challenging edge cases.
