Or how about just sticking with CSS selectors and CSS syntax for the metadata file? MSS?

div#container ul.top-nav { metadata: DC.Title }

Of course, HTML already has a element that you’d really want to map to DC.Title, and a page that doesn’t provide that probably has additional problems.

One nice feature of your idea is that it’s not incompatible at all with RDFa (my preference) or with HTML5 microdata. DC metadata could be mapped to RDFa attributes as well as to HTML element text.