Instead of using RDFa it would probably be easier to use Microdata (W3C spec). It's an HTML extension that follows the same goal as RDFa and is more used on the web[1]. The big advantage of using it is that the MediaWiki parser already supports Microdata tags so no change to the parser would be required to implement such system. It is already used by a few wiki to embed easily machine readable data in wiki pages. It also has the advantage of not conflicting with the Parsoid HTML output that is using RDFa for annotations (e.g. to tag that a node is a template call...)..
You may also want to have a look at schema.org that is a project endorsed by W3C and run by search engine companies to create a shared vocabulary for RDFa/Microdata/Embedded JSON-LD.