A new XML standard has been proposed for publishing faceted metadata. XFML.
eXchangable Faceted Metadata Language. XFML is an open XML format to publish and share faceted metadata for websites. It allows for easy creation of advanced, automatically generated navigation for your website. You can even automatically generate links to related topics on other websites. It also allows for merging of metadata between different websites.
This looks promising for publishing meta data that can be used by other web sites and/or user client software. After reviewing the information on the site it does not appear that they borrowed anything from the Zthes DTD for xml representation of a thesaurus. It seems to me that creating linkages between the two could make both standards stronger.