It adds some simple TEI tags to the wikitext markup. The code isn’t very good but may be improved (it’s a very simple and small extension).

I don’t think it’ll be a good idea to add it to Wikisource because it will make even more differ the Wikisource wikitext from the "standard" wikitext and so will make the integration of things like the VisualEditor more difficult. In fact, the question is: "Do we want to have our own powerful Wikitext or to keep the standard Wikitext less powerful but far more standard?"

Thomas