Since both RDFa and Microdata support the same underlying data model, and it's likely to take some time to resolve which will be the eventual winner, perhaps we should decouple the generation of the final HTML output from the markup of semantic text in articles.
Since it makes no sense to implement yet another incompatible "semantic wikitext" format for internal use, we will probably end up using something that is pretty close to one or the other, buried inside templates, to perform the actual in-wiki markup. Given this, is it worth considering which is easier for template authors to write, and which is easier to convert to the other -- RDFa to microdata or vice-versa?
-- Neil