A majority of my concerns were resting on XML Schemas and the like—or even OWL (!)—but even recognizing what you mean about XML being semantically neutral it's

A majority of my concerns were resting on XML Schemas and the like—or even OWL (!)—but even recognizing what you mean about XML being semantically neutral it's still... semantically dangerous. The issue at hand where attributes and elements can serve very similar purpose is a great example. In a technical sense XML does not suggest anything about the relative meaning of these two bits, but with near universal acclaim they're used as "metadata" and "child data" whatever the speaker might believe those to mean. In spiritually embracing TIMTOWTDI, XML has created a playing field where semantics are by default ambiguous and have to fight their way out of that disadvantage. In some sense, XML-without-semantics has too much structure and this creates a minefield for laying meaning atop it.