Fall of Cadia

So the new prep release just went up for preorder, what's everyone's thoughts? So far we know there is going to be a black crusade of sorts, the necrons are involved, Cadia is going to bolster their defenses they seem to know about the attack, space marines are going to have a hand in it. I believe the necrons will ally with the Cadians but have ideas of their own after the chaos invasion is knocked off the planet again, although if chaos does fail that puts abandon past the point of return to help lead another crusade, that's a dead horse for GW you can't keep having him fail, folks will grow bored so more than likely they're going to move the story forward.