I think we'll realistically see a revisit of Nurgle and Slaanesh before we get a new Chaos army, but I do think a Vampire army is likely. That said, I think Neferata should run it. For Destruction, I think they could do a Creatures of Chaos style army covering various new monsters who worship or embody various aspects of Gorkamorka, or an army of Elementals inspired on the old Incarnate Elementals from FW, the concept being primordial beings of the Realms aligning with Destruction to remove the unnatural (in their eyes) influence of Grand Alliances Death, Chaos, and Order.