As for Kellhus deducing the radiation risk... He probably has some limited knowledge of Tekne, and has deduced the basic laws of physics. He could probably use his Metagnosis to peer into the nuke and deduce how how it worked, and then go from there.

Nah, I doubt that was the first nuke ever used. So there should be old Nonmen stories partly known to the Mandate.

I have to say though, I've seen a detail mentioned before that is becoming more and more salient to me: if there are so many Sranc in the North, so many that between the Dunyain, the scalpers, the Great Ordeal, there's still an incomprehensibly vast amount of them... By all rights the Sranc should have eradicated mankind a long, long time ago. If there's an entire subspecies of them dedicated to leading their roving bands, if the Erratics under the Consult have mustered a great many of them as an army, then even despite the No-God's absence I just can't think of why they've taken so long to reduce the population to 144k. The Consult have had this one in the bag for the last couple of centuries at least, why on Earwa have they been waiting for mankind to muster its forces and cut their way into Mordor?

Both the ten yoke legion and the force exterminating Ishual were led by Nonmen. Nonmen are irreplaceable and there is a lot of ground to cover.

Also after this chapter it finally clicked for me. The Dunyani are an ancient plot by the Nonmen kings, Mek in particular. Seswatha is/was also into it. Its the perfect conspiracy because no one remembers it. Why was Mek there in the prologue? So he could get the new Dunyani and transport him south. Just as he did with Moe. And maybe the Latter Prophet? That would make the Trapper the one who derailed everything.
Why does Seswatha have to be involved? Because he knew where Ishual was, Mek didn't. When did he join? At the walls of Daghlish(sp). It wasn't a place he should have been able to escape from under his own power.
This explains several things:
The Dunyani extinguishing magic and history. Otherwise they would be unmanageable. No matter how smart you are, you won't catch on to magic spies if you never consider the possibility.
Cleric sounding like Khellus.

No idea what the purpose is, but the idea of Mek burning down cities in particular patterns just so he can remember his part of the plot has a lot of appeal. I propose that he staked the population of Daghlish to the wall as a giant screaming post it note.