Note that web intents is not a wire format -- data is exchanged within the browser process, and not transmitted over the network. The format of exchanged data types, though, is obviously of great importance. The task force has mainly been concentrating on the API, but we're starting to do more work with messages and data types now, with these wiki pages, the UPnP work that Claes and others are doing, and the Gallery API proposal from Jungkee Song:
http://lists.w3.org/Archives/Public/public-web-intents/2012May/0002.html