XML/XSLT is a huge mess of a code base to implement correctly - especially XML parsing has been a fruitful source of exploits in the past. And it's not used in practice these days, it's been ages since I saw that used on the web out of RSS/Atom feeds (which are practically dead, for better or worse) and Java-based CMSes.

So from a technical standpoint, I do understand those calling for it to be eventually removed.