The Wikipedia DTD would be an extension of it, and would include features not every other wiki supported. Mediawiki would be able to innovate and extend this DTD without affecting the standard. It would remain clear which wikitext was portable between wiki software suites, and which was confined to the mediawiki universe.
The spacetime DTD, ecoregion DTD, person DTD, and other features required for the first useful map and the first useful person profiler functions could be part of the first Wikitext DTD. The simple ideology of Wikitax would be used to guide its further evolution and integration of wiki, blog, crit and other user functions.
The article Wikipedia DTD contains a prototype of a possible Wikitext DTD.