Go with me here...
We know that the Legion is interested in Azeroth as it holds in its core the 'last' Titan. Whether or not Azeroth *is* that Titan or simply an egg for the Titan is debatable, but a debate for another time.
So I'm sitting here with my tinfoil hat on and I'm thinking 'what if there are others?'. We know the Titans scoured the universe looking, unsuccessfully, for a planet with a World Soul - ie; a developing Titan - until they found Azeroth. We also know that Sargeras killed the Pantheon and has endeavored to destroy Azeroth, and indeed all life in the universe, as a means of defeating the Void Lords with some finality. We also know that it was Sargeras' Burning Legion that corrupted the Orcs and brought them to Azeroth, destroying Draenor in the process.
What if - and this is a big 'what if' - Sargeras was killing two birds with one stone? What if Draenor, like Azeroth, held a World Soul, and that Gul'Dan destroyed it when he broke Draenor apart. What if that's what the Legion is trying to do again in the Tomb of Sargeras (with their massive portal being a 'wound' in the world)?
Is it possible? What would the ramifications be if this were true?
/tinfoil