The extension I've always wanted is a one that makes every link to a modern story on the New York Times, CNN, ESPN, etc. load using their same websites from like 2004.
I tried "Make this page look like the 2004 version of CNN" and it did update the theming to be older but it didn't have the true reference, so it just made up the old style.
We don't currently have a way to provide a reference during generation, but if I were you, I'd personally try downloading the old page archive and a new page archive, throw them both in codex/claude code as context and see what it can come up with. Wouldn't be surprised if it could do a decent job writing a converter.
Somewhat tangential: I have had luck with more generic retheming, e.g. "Turn Google into a 1970s era CLI " (https://www.tweeks.io/share/script/8c8c0953f6984163922c4da7) or "Turn LinkedIn into a 90s era Neocities site" These aren't the most useful, but they are fun!
https://web.archive.org/web/20041207071752/http://www.cnn.co...
Make every new page I load look like this, or a slightly cleaned up or mobile-specific version.