Interesting concept. I don’t think that I’d buy any to store, even if I had the space, especially a diesel, but I agree that prices will hold strong on petrol and diesel cars and probably increase as the cut off date draws nearer.
With the average age of cars on our roads being 9 years (so 50% are older than this), if you do the maths starting with the 2035/40 cut off dates, it will be perfectly easy to still be driving an ICE car until around 2060, which is 24 years away. I suspect that a lot of drivers who are 60 or over will easily be able to finish their driving careers in an ICE car should they wish to and, of course, many will.