I don't think safety is even an issue here - I think self-driving cars will be MUCH safer by default, so this kind of safety precautions (turning the front seats) will probably not be needed. I am thinking more in terms of travelling comfort (talking with fellow passengers, playing cards,...).

That said, I agree with your comment on motion sickness. I am guessing that there will be much research in this area - it might be possible to eliminate sickeness by properly adjusting tilt of the car through curves and when braking / accelerating. It would love to play with this, though not in a role of a tester. ;)