Just for clarity
[url]http://www.warseer.com/forums/showthread.php?282133-Jes-Goodwin-at-Dark-Eldar-Launch/page4[/url]
2010, and I dont even think thats the earliest time this has been mentioned
EDIT:
Im pretty sure the 2004 date for DE was from Jes's concept sketches, which doen't mean that the sculpting had been started, merely that he was exploring the design direcction to take the army. slightly different emphasis.