That seems like a good proposal, but it should have been considered from the start to get people onboard: not scaring them into thinking they'll end up just paying more.
I'm not saying there's an easy solution, but it does seem like they're doing this upside down, and it will create nothing but resentment, anxiety and stress.
This must not be a burden on people who can't afford it, even if they are a major part of the problem. Make it cheaper to get a new EV, then to buy a second hand diesel car -> that's how you will fix the issue, and it's not by making diesel and diesel cars even more expensive.