This is an interesting idea -- Daniel over at Marenkay.com is the creator of phpArmory, which is the closest thing we have to an official API for Blizzard's Armory site, and he's now turning his eye towards unofficial databases. Sites like Wowhead and Thottbot are extremely informative, but the one thing they don't allow is player access directly to their own data -- obviously they have a monetary interest in keeping their information on their site. But an open source site, as Daniel says, would allow players to get at that information whenever and for whatever purpose they wanted.
Very interesting idea, and it sounds like he's got the coding chops to do it -- he's already got a working prototype together, apparently, and he's taking suggestions on where to go next. We'll keep a curious eye on this one. Competition is always good for customers, and while the current database sites might not be interested in an up-and-coming open source version of themselves (actually, the great WoWWiki is pretty open already, though they don't really collect as much numerical information), having widespread open data on drops, kills, and gear would be very beneficial for players. This could turn out to be a very important and helpful project.