I really like XML a lot; I've gotten large numbers of people to use XML & XSLT, where I work. XML is dated, and it is gross. Here's the two things the XML ecosystem nailed, which tie me to it:

1. A dedicated tree-based transformation language (XSL); and,

2. Axis-queries (Xpath).

If I could Xpath all-the-things, I'd be a happier human. Although, I also feel like I should be able to SQL all-the-things, too. Maybe I'm just a sucker for structured-data query-languages?

XSLT is garbage tho.

XSLT the syntax leaves a bit to be desired. There's also a number of highly questionable default behaviors that are really unfortunate. OTOH, the concept of a term-rewriting tree-matching language is pretty great.

Also namespaces. When you need them, you really need them.

Replace xml with anything else. You're not writing XML. It's just a format used by a layout editor. The issue with this strategy is merge conflicts and diffs that make little sense to a human reviewer.