Finally got around to reading your article – fantastic stuff. And, yes, it does make more sense to semantify BuddyPress rather than WP. I am very interested in getting involved with these efforts. I am presently swamped with getting the second edition of my Web 2.0 book finished, but when complete, am starting on the Web 3.0 book. All of the issues you tackle are so important to get out there to laymen – I am so excited to get moving on writing about them…
I am game for getting involved in such a project. What frustrates me about Facebook is that they had the opportunity to link into the LOD cloud and did not take it. Their “Open” graph API pirates the concept of microformats, RDF, and schemas that have been around for years. They pretty much just took the ideas and made their own version. Bad form, I say!
What is missing from this conversation, though, is the idea that a distributed social network is not as much about where the data is and who controls it as it is about how the data is defined or “marked up.” So, yes, each person has that “virtual calling card” you define above, but it is in a standard XML file like RDF using a specific schema or “vocabulary” common to people who use a particular service. That RDF file, though, belongs to me, the user, and I can choose to add my affiliation with a specific network to that file or not.
Seems to me that what Mu (or the very excellent WordPress 3.0) needs is its own “vocabulary” within the LInked Open Data cloud to be a truly “open” distributed network.