Utopia? Did you read the last sentence of my comment? I think a self-driving car future is a future with disempowered individuals in a neo-feudal transportation world. It sounds terrible to me, but I think it's likely to happen (at least in the US). There are practical and economic advantages in that future and some large existing economic players who can profit from it.

I'd tend agree with your comment in the short term. Moving my daughter's child safety car seat would be a pain, for sure. Longer-term I would expect to see modular standards emerge for child safety car seats. You lock your child's seat into the standardized base that's hiding under a seat cushion in the back of the car. There are already stroller / pram systems that incorporate the child safety car seat, so I could expect that market to boom, too.

Moving things besides yourself is something a lot of people in urban areas already do with public transit. With a private autocar service it's more likely that you'd get more space than on a subway or bus, so I'd think it would be even easier to move more than just yourself. I would expect a rental option to let you keep the car with you, as opposed to it returning to the fleet when you reach your destination.