I love XSLT. I released a client-side XSLT-based PWA last year (https://github.com/ssg/eksi-yedek - in Turkish). The reason I had picked XSLT was that the input was in XML, and browser-based XSLT was the most suitable candidate for a PWA.
Two years ago, I created a book in memory of a late friend to create a compilation of her posts on social media. Again, thanks to XSLT, it was a breeze.
XSLT has been orphaned on the browser-side for the last quarter century, but the story on the server-side isn't better either. I think that the only modern and comprehensive implementation comes with Saxon-JS which is bloated and has an unwieldy API for JavaScript.
Were XSLT dropped next year, what would be the course of action for us who rely on browser-based XSLT APIs?
XSLT, especially 3.0, is immensely powerful, and not having good solutions on JS ecosystem would make the aftermath of this decision look bleaker.
"Why not use ActivityPub?
ActivityPub is a federated social networking technology popularized by Mastodon.
Account portability is a major reason why we chose to build a separate protocol. We consider portability to be crucial because it protects users from sudden bans, server shutdowns, and policy disagreements. Our solution for portability requires both signed data repositories and DIDs, neither of which are easy to retrofit into ActivityPub. The migration tools for ActivityPub are comparatively limited; they require the original server to provide a redirect and cannot migrate the user's previous data.
Another major reason is scalability. ActivityPub depends heavily on delivering messages between a wide network of small-to-medium sized nodes, which can cause individual nodes to be flooded with traffic and generally struggles to provide global views of activity. The AT Protocol uses aggregating applications to merge activity from the users' hosts, reducing the overall traffic and dramatically reducing the load on individual hosts.
Other smaller differences include: a different viewpoint about how schemas should be handled, a preference for domain usernames over AP's double-@ email usernames, and the goal of having large scale search and algorithmic feeds."