Blizzard has scrapped many of raids in their time. Either due to resources, or a change of story, these instances never have, and most likely never will, see the light of day. But out of all the ones they have scrapped, which one would you like to have seen?
Me? The Utgarde Pinnacle raid. The finish to the Vyrkul storyline and Ymiron was incredibly underwhelming, especially for such a mysterious Titan race.
EDIT: Either that, or the never before heard of Abyssal May ;D (spelling errors ftl)