It's not about a "gotcha." Browsers once supported the GOPHER protocol but dropped it around a decade ago. This serves as an analogy: if users don't use XSLT/XML daily, browsers may eventually drop support for XSLT - supporting features cost money

That's not a great analogy. Firefox once supported RSS feeds as live bookmarks and dropped it, and not because people didn't use it, because people did use it and bemoaned its loss for years afterwards.