As the old saying goes, if it isn't broken then don't fix it. I have nothing against XML, but I can't stand the hype that surrounds it. There is no logic in the idea that everything must be XML. If you have a piece of software like Litestep, that has an existing, working data format then switching to XML is likely a waste of time.

Think about all the work it would take to make LS configuration XML-based. Large parts of the core must be rewritten and debugged. All the config API must be replaced and, consequently, all LS modules must be updated. Everyone has to update their themes. And we must write tools to edit the config files, because XML is not user-friendly.

Then after all that work, you have a system that does nothing more than it already did. Personally, I'd rather spend my time working on real features.