Ian Davis proposes "Embedded RDF", a microformats-inspired path to metadata-enriched HTML. Unlike microformats, his approach can utilize a single generic transformation script instead of one transformation for each format (or micromodel if you prefer Danny Ayers' terminology), which is closer to RDF's idea of freely mixable vocabularies.

I had some hopes of RDF/A but stopped following its progress several months ago as it didn't seem to provide an easy way to really bridge the gap between HTML and RDF. My use case was (and is) to be able to markup html in a way which allows me to automatically (and without too much effort) generate context menus or tool-tips