I like the idea, but I think it would be better to have a way to generate the .xml file automatically. This way it is easy to keep the file up to date with each new WoW release and there is less chance for errors when entering all the functions.
Maybe ask the people of wowprogramming.com, wowwiki (maybe wowcompares??) if it is allowed to write a script to scrape the API pages. Then it should be (relatively) easy to generate the .xml file automatically. Or maybe they even have the data in some kind of raw form that is used to generate their webpages.