I believe it'll happen quicker than you think. Even if we can't move beyond having to create and maintain detailed road maps, once the concept has been proven to work, you can expect many companies simultaneously jumping to map their local regions. That's one thing capitalism is really good at - distributed, simultaneous deployment of solutions that have money-making potential.
I hope you're right. I could see that happening in warmer climates. But what about when landmarks and points of reference are covered in snow? GPS is not accurate enough to be used as a sole reference, you need a visual/LIDAR reference to back it up.
The system will have to work in 100% of circumstances before laws will be changed to allow for driverless cars. I could see that happening in 20 years, but I really doubt it'll be on the streets in 5 years like Elon Musk and others have suggested.
Construction alone is going to make it extremely difficult, unless there is a system such that the cars know where construction is taking place and actively avoid those routes, but that is not always known.
