That phrase dawned on me at some point yesterday during CSS presentations - it seems like the entire world is being configured in XML. Just about any enterprise software and many development frameworks have their configs in XML, I have even started to see benchmarks on apps that included lines of code together with lines of XML - it's been elevated to a first class citizen in code metrics! But the fact is that it's becoming less and less runtime config and more and more business logic codification.
So I think that any enterprise developer worth their salt will build and maintain skills in XSLT, XPath, and XQuery. These are not the hot technical skills that will raise your bill rate or necessarily float your resume to the top of the pile. But I think they are going to be seen as core skills before too long. And you just might be the superhero who rescues your team someday when migrating away from a mountain of proprietary XML configs.