The main thing that seems unaddressed is the UX if a user opens a direct link to an XML file and will now just see tag soup instead of the intended rendering.
I think this could be addressed by introducing a <?human-readable ...some url...?> processing instruction that browsers would interpret like a meta tag redirect. Then sites that are interested could put that line at the top of their XML files and redirect to an alternative representation in HTML or even to a server-side or WASM-powered XSLT processor for the file.
Sort of like an inverse of the <link rel="alternate" ...> solution that the post mentioned.
The only thing this doesn't fix is sites that are abandoned and won't update or are part if embedded devices and can't update.
I really appreciate Cloudflare not putting SSO behind a paid subscription because using their Cloudflare Access product with Github SSO has been the easiest way to secure my personal services running on a VM.