Author here - loving all the discussion! I was a bit intimidated to submit this to hn - I'm humbled that someone else thought it was worth posting. Of course, happy to answer any questions anyone may have!
> You'll need to enable Javascript to see this section sorry! There's a slider that lets you see how changing the delay in a GIF file will affect the end results. It's pretty cool.
Thank you: this is an excellent way of handling the situation.
(For myself, I take care on my site in the few places I ever use JavaScript, and also even vary my content in feeds where it depends on JavaScript or site styles, which I’ve never noticed anyone else do. make-and-git-diff-test-harness and dark-theme-implementation are slugs of two sample articles that both vary by JavaScript and feed, I won’t drop links.)
Unfortunately I didn't document the process at all and have forgotten everything, so I can't give much useful info, apologies. Just know that there is pain down that path.