I love the mental image of a whole highway full of cars slamming on their brakes to let a leaf blow by.

How would a full switch to automated cars work anyway? Would they require different roads?

If their functionality included stopping on a dime at a duck on the road, and human reaction speed isn't equivalent, it isn't safe to human drivers. But cost and manufacturing has to factor in before we can just replace every car on the road. People still drive 20 year old cars.

I expect it will be a mixture of carrot and stick like any good phased replacement. Dedicated lanes (since they can drive 2ft from the car in front) and higher speeds because they are able to cut the reaction time down so much lower.

Eventually making it mandatory for some classes of roads (motorways / highways).

At some point in the very distant future your classic car will only be good for showing off on track days or classic car meets.