He did not touch Bain, but the tauren could almost feel the fire of the other's banked rage churning. The gray-skinned orc's eyes glittered, their coldness not tempered the heat of his anger but augmenting it. And Bain felt a prickle of unease. Who was this orc? (Tides of War p. 24) - That was the line that really stuck in my gut, I got the feeling like whoever Malkorok is, we've met him before.
Malkorok is missing two fingers. Likely that one represents the Legion's defeat in the War of the Ancients, and the other represents its defeat in The Third War.
Malkorok isn't comfortable with the daylight provided by the harsh sun of Durotar. The given reason is that he's been in Blackrock Mountain for 30~ years, another alternative is that he's been in the dark depths of the Twisting Nether for twenty-five-thousand.
Kil'Jaeden organized and corrupted the original Horde via the same method, by pretending to be an Orc and whispering in the ear of its leader.
The Draenei starting cinematic states that the prophet Velen has foresaw a coming war between shadow and light and Wrathion's quest in Pandaria shows Azeroth with giant meteors crashing into its surface and laying waste to the land - very reminiscent of the Burning Legion's Infernal's preferred method of interstellar travel.
The purpose of Ner'Zhul and the Scourge on Azeroth was originally to soften any opposition the Legion might face and herald their arrival, that threat has been subdued. Starting a war between the resource starved post Cataclysm era factions of Azeroth is a good backup plan.
At the site of the Focusing Iris' theft this is said: "As Kirygosa and the others sniffed the air, they caught the lingering stench of demonic activity..." (Tides of War p9) and to be fair they also found evidence of arcane activity so the fel taint could be generic Horde warlocks.
Now take apart everything I've said bit by bit and point out why I'm wrong. That's what I'd do to you ;) It's just a hunch.