My latest theory!
Given Ewing's overall work in Immortal Hulk and other cosmic stuff, specifically in terms of the One Below All, the counterpart to the One Above All, who is essentially the prime mover/creator of everything that is....and the fact that he typically portrays the One Above All in a meta sense, living in the House of Ideas, encompassing all narratives & manifesting in the form of narratives and creative ideas....
And given that Ewing very deliberately used word choices like adversarial when talking about Annihilation and its origins, drawing connections between it and The Adversary, as well as the solicits that show Resurrection of Magneto will be including the Shadow, the primordial force/entity that possessed the Shadow King for centuries....
I'm positing that all three are connected, and are actually three out of seven entities who serve as the chief manifestations or agents of the One Below All....
Embodying the seven fundamental narrative conflicts that drive storytelling in general.
The Shadow, who pits people against their own worst natures....is Man vs Self.
The Adversary, who pits people against a higher power, an entity beyond the natural order....is Man vs Supernatural.
Annihilation, who pits people against each other, turning sister against sister, husband against wife, army against army....is Man vs Man.
With the other four fundamental conflicts being Man vs Technology, Man vs Society, Man vs Nature and Man vs Fate.