@ Kosoter - Love the idea that Kosoter is Ciphrang. Who else could be? Anyone we don't have internal monologue on could be. Kelmomas? I bet Kellhus would find a lot of use for this kind of possession. But what if Kosoter is possessed independent of Kellhus' Daimos? Other people could be using this tactic.
Needless speculation:
Kellhus had Iyokus ciphrang-possessed long ago and someone else. The two heads he keeps on his belt are a device for holding the Ciphrang in their current bodies. The other one is Kosoter. Plus Kellhus has like a whole trunk load of them under his bed.
The Consult replaced Saubon with a Ciphrang ages ago.
The Dunyain captured a Ciphrang in the body of a little boy years ago and have slowly, meticulously convinced it that it is a human named Kellhus.