There has been a prominent announcement from Google, Yahoo, and Bing that they are going to support microdata for their http://schema.org vocabulary. While I believe they do intend to support RDFa for that as well at some point in the future, there seems to be some momentum behind microdata, so hopefully we can combine the RDF and microdata efforts to provide data interoperability to the widest range of consumers.
Entity referencing fields that are based on Entity API work perfectly for RDFa without modification. The field wrapper contains the attribute name and the output of the field formatter is used as the value. Unfortunately, because microdata requires that both the attribute name and value be included in the same tag, we need to make a minor modification for proper microdata Field Collection values.
I will attach a patch that includes support for the API in its current state. I don't recommend committing this until microdata module moves into RC, but I wanted this patch to be here so people could test.
PASSED: [[SimpleTest]]: [MySQL] 78 pass(es). View
PASSED: [[SimpleTest]]: [MySQL] 77 pass(es). View
FAILED: [[SimpleTest]]: [MySQL] Unable to apply patch 1199028-03-microdata.patch. This may be a -p0 (old style) patch, which is no longer supported by the testbots. View
FAILED: [[SimpleTest]]: [MySQL] Unable to apply patch 1199028-01-microdata.patch. This may be a -p0 (old style) patch, which is no longer supported by the testbots. View