This might be very interesting if it's implemented in a sane way. Unfortunately there doesn't seem to be a very widely-adopted standard in the world of open data for now..
RDF has been adopted by some pretty big data websites, and apparently that's one of the formats they plan to support: The data will be exported in different formats, especially RDF, SKOS, and JSON. http://meta.wikimedia.org/wiki/Wikidata/Technical_proposal
The question is which schema, ontology or vocabulary will they use to express their data? Who will develop it? Or will they reuse other vocabularies? How do they intend to extend them? If they are RDF based, how will they project to JSON given that there are a dozen different conversion methods?
How can that document not cite DBpedia, a project that is extracting structured data from Wikipedia infoboxes and has years of experience in doing that?
The fact that their technical proposal document is quite confused about these ground technologies makes me fear that there is more wishful thinking than past experiences.