It also assumes a linear trend continues. I think that is probably true if nothing changes, but there is a lot that could change that. The most likely change be joining the EU's "made in Europe" car policy which would mean far higher tariffs on Chinese EV imports.
Why would the second hand market cave first? You can buy second hand ICE cars very cheap. There are lots of second had ICE cars for under £2,000 (look at places like Autotrader). Will people be able to buy five year old EVs for that price? Assuming batteries law reasonably well, I expect EVs to keep their value better than ICE cars.
its very clear at the moment that the move to BEV is being lead by new cars. The second hand market will follow because sales of new cars determine what is available second hand a few years later.
On the other hand a lot of the growth in EV sales is coming from Chinese manufacturers so it will probably slow it down a bit - but less than I would have guessed.