Perhaps Kellhus ... was gradually suborned by Ajokli without his full knowledge or control. Perhaps by the very end he was no more in control than Sorweel was in the moments before his death. Just a puppet for who knows how long, right up until Ajokli took over in truth.
Which is exactly the sort of deliciously ironic punishment Ajokli-Who-Was-Cnaiur would have wished upon the one who had made a puppet of his soul twenty years before, surely?
I think it is worth remembering that Kayutas and Serwa seemed
really worried about the prospect of Kellhus going into the Golden Room alone. It seemed to me like he'd warned them not to allow that to happen. Just a shame a dragon and
99 100 chorae got in the way. Yeah, we all assumed it was the possibility of
the Consult subverting Kellhus that they were worried about, but maybe it was his possession
by Ajokli that they were supposed to prevent?
Heck, if Mimara had gotten up there with a chorae, she could presumably have banished Ajokli like she did to the Wight of Cil-Aujas. Maybe that was a contingency in Kellhus' plan? But, again, circumstances got in the way: Mim went into labour early, which Kellhus could not have forseen (Yatwer's final gambit, maybe?)