Lol.
Kellhus owns circumstances.
Also, there's no reason to believe he could just "join the Consult." He probably couldn't take on the Erratic Quya, let alone Aurang, Aurax, Mekeritrig, and Shauriatas as well (much less, stop by for tea and tell them how he was mistaken for outing their skin-spies).
But if Kellhus wants a new toy, I'm sure he'll do it on his own terms. Plus there's no reason to think he doesn't want the Tekne to use to help for humanity.
Aside, I'm glad someone else thinks that the Great Ordeal is the ultimate historical chance for repeat Trauma for the Erratic Nonmen.