Earlier quoted context omitted.
With a huge fleet of self-driving cars, there would be enough capacity to have permanently configured cars for child seats, bike racks, dog areas, etc. eg. "I need a 4wd vehicle for 2 adults and 2 bikes to take me to X park at 10am tomorrow."
Not without seriously increasing the costs for car rental. The cost savings for car rental are predicated on increased utilization. Increased utilization is predicated on each car having more people using it on any given day. And these things don't scale infinitely -- each car can only serve a particular locality. The number of variations that you propose is a fast geometric progression. Kids 0-12 months or so need d…
But I don't need or want to buy a wheel, batteries, cameras, lasers, etc. Those also should be upgraded as technology gets better but my box doesn't really need to be anything but a box.
So what if I could sit in my box and have a transporter thing come over and clip onto me and take me away? You could have child seats and I could have a lazyboy chair, or I might need 8 seats and you need storage space.
This would then let the actual transporters take other types of cargo too, rather than having a people vs items split. It would allow a pony-express style swapover rather than needing huge range in a single one. It would even allow completely different types of transport, what if my pod could just be clipped onto a big train and whip me to the other side of europe?
This would all likely have other downsides, but is a fun thing to think about.
TL;DR shipping containers