If all newly produced cars are self-driving cars in 10 years, I think it is reasonable to ban non self-driving cars 10 years after that. So 20 years sounds about right. It's not that long for such a fundamental change.

And yes it will create its own problems. Like if these cars get hacked, they will cause serious damages.

So if you think the timeline is 20 years at best then we need that present self driving cars be able to drive on present roads with human driven cars, pedestrians, bikes, holes in the road, some bad marked roads, roads without markings, roads with a bit of snow, heavy rain,fog.

Adding some extra markings, special electronic markings for this cars is not a solution, and in this 20 years since the traffic is mixed you can't consider lifting the speed limits or changing the intersection rules, so I don't see how it helps the traffic (except maybe on small streets if you consider that people won't want to own their car and will use any random car. this random cars should be super clean and cheap to make people not own their own)

Or maybe having a population with no hard challenges in their youth, like learning to drive and surviving. Seems to lead to people incapable of handling adulthood or developing judgement about risk.