I don't think that we can safely assume the Azjol'Nerub raid is forever lost to us. Yes, it was originally meant to be a part of the Wrath of the Lich King storyline. But ever since I finished the Klaxxi rep grind, I've been more and more convinced that the first raid tier of either the next expansion or the one after will be a trio of raids [much like how all expansions seem to have three distinct raids for the first tier, followed by solo raids for their later tiers; odd, that]: a new Ahn'qiraj [hopefully new and not a rehash, but who knows], Azjol'Nerub, and some new Mantid raid.
We're currently aimed at two end goals for the game: Sargaras and the Old Gods. World of Warcraft doesn't have an infinite life ahead of itself. It could well be that Blizzard has seen the writing on the walls and is allowing us to move towards a specific endgame, where we take down both of those final threats before the game ends. And think about it, if you left the game, wouldn't you come back to face Sargaras? I would. That's why I think the Old God expansion may be next, with the Burning Legion expansion last. Sargaras would simply be the biggest draw.
Anyway, for an Old God expansion, who else would we fight first but their foot soldiers? The bug races of Azeroth have been their grunts since the beginning. So I fully expect to see a Nerubian Raid soon.