Red Thread Games, who will focus on the world plot and fantasy elements. Graphics and gameplay can remain with Square Enix. Character work / dialogue can be shared.

Alternatively, for a more major group, Ubisoft.

Alternatively, if it's a "complete" merge where all aspects are shared between the two groups... Mistwalker.

Alternatively, I'd love to see what Naughty Dog would do if they were advisors.