In the meantime, can anyone think of how to make this work as a javascript hack?
Sure, and I can even show you screenshots of me using it. Like the saying goes, "the future is already here, it's just not widely distributed yet" :-)
You can check out the experimental screenshots, and an explanation of how it was done, here: http://nickj.org/Experiment_with_Suggestion_Searching_on_Wikipedia
As you can see, it definitely has rough edges, but the basic concept works well. The main obstacles to normal people using it are the JavaScript cross-domain restrictions (details below), and updating the current MediaWiki search area to have the option of using suggestion searching.
I was talking about integration in *wikipedia*, but if I understand correctly, you are talking about doing query on my web site from wikipedia search box ? If yes, it will probably be a little bit difficult because of browser protection, you can not use http request in javascript to another host.
Ok, so that rules out integrating via a user script until the search database is hosted at wikipedia?
Yes, that is a problem, and to get around it I configured my proxy to silently rewrite certain requests so that they look like they come from en.wikipedia.org, but in reality they come from Julien's site. That allows me to get around this restriction (and probably GreaseMonkey would let you do something similar), but it won't be a viable option for 99.9% of people. For them, the suggestions need to come from the wikipedia (even if it's just a temporary two line script which bounces the request straight off to Julien's site).
All the best, Nick.