But some people will be on the road more often than others, so the likelihood of an incident will be different.

I think it would be much better to add a premium onto the fuel the car uses and all claims would go to a central organisation.

Self driving cars should level out risk we currently have in different driving demographics i.e. a teenager in car is as likely to crash as someone who has been on the road for 20 years. So it's not like you'd be paying more "liability coverage" than you should.