Adding Topic Maps to MW base software could be a winner -- it can generate a wiki-site map (some think WP needs one!); it can be used to corelate the contents of documents loaded into a wiki (like conference proceedings) with a wiki's topic map; and would make a cool tool for any page in a wiki, most clearly on a user page. It's perhaps a smart strategic move - ISO 82250 Topic Maps are the fruit of SGML/Hytime n-ary models that 'lost' to RDF triples back when. Being a superset of RDF, TMs can type associations between articles while capturing all infobox data.
Topic maps may be a compelling FUNCTIONAL upgrade for MW as it captures subjects of an article for the first time. Given topic-map to RDF transforms amid continuing W3 research, this could be enough for the semantic world. By adopting say the Lib of Congress' Subject Headings, a wiki like Wikipedia could play an important role in the semantic web. The current situation with Wikipedia is that it's hard to have a large library of information without a subject catalogue... right now, wikis have an author catalogue sort of, fine for smaller hadcrafted wikis but doesn't scale well for many.
Since other platforms now have maturing topic map extensions I'm worried the impact on wikis not to have that technology.
John McClure