Mostly i wonder what Sil looks like and if he differs much from his two warlords and in what ways. we know he's big because he wears armor adorned with 'the festering bodies of his foes' which at that time were the Nonmen, and they weren't small.
thoughts? stuff n' all?
I've always imagined Sil to look like Nito, the First of the Dead:

Basically, for those unacquainted with Dark Souls game, Nito is both a god and a giant skeleton wearing common-sized skeletons as some sort of cape or trench-coat.
So. A thin giant with initially-elegant build, who in the end looks like an indomitable mass of flesh thanks to all his slain enemies/comrades hanging from his body?
I think the oyster skull thing is likely the remains of a past graft. Since they are often referred to as a species wide rewrite, I'd guess that most major traits like that would be shared.
I still feel like the oyster heads and gills point to an aquatic past. My pet theory, of course, is that the first limitation they sought to overcome was their underwater nature.
Considering
weapon-races and all that guesses about Arc being sentient creature, I suspect inchoroi are just a members of a
warrior-race with no independent history aside from their crew-membership. Also, it could be the reason behind their damnation. They can't even relate with corresponding metaphysics because of their artificial, narrow-specialised and thus flawed, highly-incompatible origin. Being srancs to the Arc, why should they have a commune with the divine? Arc possibly had, but it's dead, lol.
And a crackpotty! Viscera of the living Arc was all liquid. Proto-inchoroi evolved inside among it's other natural habitants, thus their aquatic features, but later claimed the whole Arc as their own. You know, like mankind takes a planet mile by mile. So both their genocidal crusade and inevitable crush-landing were sort-of predetermined. Because inchoroi are just Arc's disease; something with virus/cancer/autoimmune image and destructive effect.