Or an active suspension that cancels out all bumps. This is actually my fantasy for self-driving cars; such a suspension is relatively expensive, but if cars are shared and autonomous, each car can be more costly.

It's not just the bumps, though, it's the acceleration. The car is inevitably going to speed up, slow down, and change direction, and I don't think there's any way of canceling that out. I'm almost certain I couldn't read in even a perfectly-suspended car without feeling sick.

Sure there is, just change the gravity vector; this is how motion simulators work.