Metadata as XML sheet in music files

The day is coming when metadata will be implemented as an XML document in accordance with an industry standard (or individual custom) data type document.

It would seem straight-forward to include an XML document in place of vorbis comments in a slightly-modified version of the flac file format. I don't know about other formats and how adaptable they might be, as most are hampered by large corporate self-interests.

Comments are fact, desired. I know of at least one standards organization that is considering this approach.