Okay, it's not quite done, and it's still really crude, but starting to take shape - I've got some basic intersections functionality running on Wikidweb - I hacked skin.php and added links to the special intersections page. The intersections are using a MyIsam fulltext index. I'm not using 'boolean mode' queries, as this seems to give more interesting results.
(look at any article page at http://wikidweb.com)
The UI on the special page itself is really ugly and needs lots of work, and once this is all done it will have to be ported to an up-to-date version of mediawiki (I'm way down rev), but *it's a start*.
Comments, suggestions, criticisms, and offers to help all welcome.
Best Regards, Aerik