As to your question 4 : Why on earth would someone who owns a petrol car NOW hold on to it for the next 23 years ?

People panic-buying electric cars NOW ? Again, why bother. People will see the range, realise it won't work for them, and walk away. Or they just won't have the space and facility to put the thing on charge (lots of people park on the road, not in nice garages with power points).

Any change in the marketplace will be driven by customer demand - as it has been for a long time. If petrol (or electric) becomes more popular - in the used marketplace in particular - then the demand for the same-sized pool of vehicles will increase, pushing up prices. Cars registered new NOW will take 2-3 years to properly filter through to the used marketplace, meaning a huge lag time. But at the same time, demand for diesel cars will drop, forcing prices downwards.

But then people get in their nice, less-polluting petrol cars, and realise that in a lot of cases they are getting far worse economy (there are exceptions) than they were in their old diesel cars. And people who did want to change to petrol cars - but now can't afford to, due to the lack of availability - will look again at the now-cheaper diesels.

It's a pendulum. Or a see-saw. With ripples coming from various directions, with differing effects. If you can predict 5, 10, or 20+ years down the line, then you're probably in a position to purchase a fleet of Teslas. If you can't afford that fleet of Teslas, then you aren't as good as you think you are at predicting the future !