The case for JPEG XL is much better than that for XSLT. On the other hand, people who program in C will always be a little terrified of XML and everything around it since the parsing code will be complex and vulnerable.

Having a background in C/C++, that was the problem I ran into when I had to learn XSLT at translation company that used it to style documents across multiple formats. The upside of using XML was that you could store semantically rich info into the tags for the translators and designers. The downside, of course, with all the metadata, was that the files could be really large and the XSLT was usually specifically programmed for that particular document and very verbose so the XSLT template might only be used a couple times.