I don't think there's much issue with copying the content of the old pages over and just making it clear that X.css has the old history.
Reading a bit more now, but a lot of the CSS porting has been simple in my experience, so correct me if I'm wrong but this seems like it will be much smaller of an issue than you're all making it out to be. Why not deal with this surge of intractable CSS requests when it actually comes and not cry wolf now?
People really out here threatening (again) to quit and join the animated foot scene wiki host because they can't be bothered to change some class names in the 5000 lines of css they wrote for a website called Fandom
mediawiki file editors general strike of 2021 🤯