Hehehe the weapon was created to kill Lich King... no sense in needing to kill him 1st like this new legendary.
It actually has nothing in common with SM, except for using "primordial saronites" + "shards", the story/purpose of it looks totally diferent. You'll use it to fight the forces in fireland, but it's not meant for it. It's a "house" for a victim of Deathwing in the middle of Ragnaros incursion and the Blue Dragon Flight betrayal/council. It does indeed start with a vision of world burning and all, but the Staff is something created in the middle of all this mess to "save" Tarecgosa.