Blizzard has a new book coming out called Warcraft Chronicle (the first volume of a series.) Unlike other tie-in books, this isn't a single narrative, but is rather a full history of Azeroth and beyond - kind of Warcraft's equivalent of the Silmarillion.
There are twenty pages available as a preview (I found it on WoWHead,) and boy are there some pretty huge revelations.
First off, it kind of determines a sort of "highest order" of beings in the universe. There are several forces at work that function in kind of dichotomies - Life and Death, Light and Shadow, Order and Chaos. And each of these opposed forces has a kind of prime representative. The Titans are Order, while the Burning Legion is Chaos. The Naaru are Light while the Old Gods are Shadow. And the Wild Gods (aka Ancients, Loa, and Celestials - which are now officially confirmed to be the same sort of thing) represent Life while the Undead represent Death.
This last one is a little interesting, as there hasn't been really one big representative of Death until the Lich King was created in relatively recent history. Yet that beings said, while young, the Lich King has more or less stepped into a position of such incredible power that it wouldn't be hard to describe it - the entity that transcends Ner'zhul, Arthas, and Bolvar - as being something on the same level as these figures of great power.
We get a few other confirmations. One is that yes, the Night Elves were originally the Dark Trolls. Despite the ominous name, the Dark Trolls were actually pretty chill people - uninterested in fighting the other Troll empires, they originally just lived underneath Mount Hyjal and then explored eastward (apparently going as far as Uldaman) before discovering the Well of Eternity and settling there. The energy of the Well transformed them into the Night Elves we know today - and this all happened about 5000 years before the War of the Ancients.
Now here's the biggest thing:
The Titans have been traveling the universe searching for more of their kin. They know that some planets contain a "World Soul," which is a nascent Titan. While their search was fruitless for untold eons, there was one world-soul that was slowly developing within a planet called Azeroth.
In its earliest eras, Azeroth was ruled by the Elemental Lords. They would fight constantly in massive, destructive battles. Yet all the elementals reveled in these contests - the state of constant war for them was ideal and utopian, even if we mortals would be horrified by it. Without warning, the Old Gods rained down from the Great Dark Beyond, implanting themselves in the surface of Azeroth like fleshy meteorites.
The Old Gods oozed out organic life in two forms - the insectoid Aqir and the cephalopodic N'raqi, also know as the Faceless Ones.
Of the Old Gods, Y'shaarj was the most powerful, and used its minions to build around itself the Black Empire. But the Elemental Lords struck back, working together for the first time and using their combined might to reduce the Black Empire's citadels to ash.
There's a lot to process here. First off, it confirms a lot of speculation about the nature of the Titans and the value of Azeroth. For all we know, Azeroth could be the home of the only nascent Titan in the universe. What happens when that Titan is ready to emerge? Are the races of Azeroth kind of screwed in that regard?
Also, from the sample we've gotten, it's not entirely clear if all organic life or just the Aqir and N'raqi are direct products of the Old Gods. If it's just those two, though, it does raise the question of where other life came from.
I've got to be honest - I've always been kind of repelled by tie-in novels. It might just be snobbiness on my part. But I'll confess that Chronicles has peaked my interest.