That would mean that either Mark would have to write an XML/XSLT parser in the kernel, or call a third party XSLT parser. Neither of these are really practical to do from the kernel. Writing your own XML/XSLT parsers is a distinctly non-trivial task.

If you want to have some sort of templated HTML in the kernel for the playlists then the format is going to have to be fairly simple to make it easy to parse.