The reason Wikipedia's search is broken isn't (only) because it doesn't take advantage of the interesting data representations you can use; it's also just a really shitty search algo. It doesn't make any guesses, it doesn't look at related terms, and it often won't bring up the relevant article unless you specifically type that article's name.

There's a huge opportunity to beautifully represent information on Wikipedia and make search easy, intuitive, and informative, but it all rests upon having a search algo that isn't utter crap. The WMF will have to fix that before any of this will have any practical benefit.

As an ironic aside, it seems that Wikipedia isn't OSS. I can find the repo for MediaWiki, but Wikipedia seems to be a heavily modified version thereof, and it appears to be proprietary. If anyone can find the repo, I'd appreciate a link.