I'm curious how many people you actually need to kill him. If it's doable with ~30, it could be an actual bonus for 25 man guilds... well, kinda, since obviously 10 mans could group up, but still 900 mln hp is quite a bit, but then again, looks perfectly doable with heroic geared group - slightly above typical heroic boss without damage buffs, but still less than Sha of Fear. Rest of abilities - no idea.
Seems to be horribly easy to grief, though. That... could get ugly.