This sold me on the secret voice debate:
And they cried together, the two brothers, shuddering within the cage of the same small boy.
As far as Kellhus' secret words that no one could hear, I think this hints at the way Kellhus may have conditioned Kelmomas to do the things he's done in his father's absence. And that Kellhus really wanted him to kill, especially the murders of the Yatwer delegation. Maybe he is actively goading the hundred to attack him, as part of his plan or maybe if he enters the carapace? I don't know but if this is the case, I feel we should have had more hints of Kellhus influencing him.
I also thought it was weird because an earlier passage makes it seem like Kellhus has never paid any real attention to him:
As things stood, it was only a matter of time. He would grow as his brothers and sisters had grown, and he would drift, as his brothers and sisters had drifted, from Mother’s loving tutelage to Father’s harsh discipline. And one day Father would peer deep into his eye and see what no one else had seen. And that day, Kelmomas knew, would be his doom …
To chime in on Kellhus' intentions and TTT, Kelmomas is actually some good foreshadowing on this. Moenghus explained TTT constitutes several things - one of which is a "lie" to rewire Three Seas society, while they claim it is also the plan to avert the Second Alocalypse. Some of us also think it's the means by which the Dunyain will achieve the Absolute.
Kelmomas and Inrilatas discuss that the real way to become an unbound soul is by doing really terrible shit to people. It's a perversion of the Christian ideal of helping others without the expectation of anything in return - it's committing atrocity knowing full well of the damnation that awaits. Kelmomas admits to his brother that he would stack suffering to the sky if he were given the chance.
Throughout WLW, we learn through the Skin Eaters and Esmenet that Kellhus has ordered some really horrible things during the Unification Wars. Maithanet says there are good Dunyain and bad Dunyain but I think the distinction is actually successful Dunyain and defectives. Either way the result is still the same - they are amoral entities that cause tremendous suffering around them. Think about all of the warfare, pollution, and suffering that occurred as a result of globalization during the Cold War. While I don't think politicians are necessarily evil, they are no less blameless for immense suffering that has occured. I wouldn't be surprised if when the Judging Eye opens on Kellhus, he is the most charred and damned soul Mimara has ever seen.
Similarly, I don't think Moenghus was evil but Kellhus remarked and confirmed in his thoughts to himself that when Moe learns of the damnation that awaits, he would war as the Inchoroi have across the ages.
Tl;dr - if Kellhus doesn't intend to carry out a Consult-style apocalypse, he probably has a lot of reasons to want to. Or maybe, more likely, Kelmomas is being set up as the villain who will try it in the third series.
