For lack of a better title, this is what I'll put this under and port it over here for perusal.
First, we have the interesting "revelation" that the Sarcophagus is a prosthesis of the Ark. In other words, it is a part of the Ark itself.
But wait, it goes further...why does the No-God need a soul in it at all? How did that work on other worlds?
Unless, the Ark didn't need a soul, because the Ark already had a soul.
Consider, the Ark made the Inchoroi to serve it. Why? It was the Ark itself who was looking for the answer to the "soul problem." So, when Seswatha says the Ark was once living, it wasn't living in the sense of breathing, it was living in the sense of it having had a soul. In other words, perhaps the Ark is the Progenitor, or rather, what is left of them.
But wait, look how the DûnSult refer to it. Not the Ark, but just Ark. That's it's name. It is a being. A mostly artificial one at this point, but one nonetheless. It died, in the sense that the soul that kept it running was gone, post-Arkfall though, which is why the Inchoroi were so lost, they were a weapon race with nothing to wield them. Because it was Ark who wielded them before, via the No-God apparatus, which was probably where the soul of Ark was. It was Ark's "brain," which is probably why it can control all the Tekne things too.
So the No-God apparatus didn't need a soul while Ark "lived," Ark had it's own soul, a soul that was seeking to find the answer to the 144,000 question. That question is what lead to it making the Inchoroi, who, later abandoned by Ark when it died in the fall, were left to try to figure out just what Ark was trying to do. A prosthesis needs something to wield it. Ark wielded it while it was still "alive" but now, some other soul needs to "read the code."
So, what kind of soul is needed to do so? Presumably one that is suitably close to Ark's original one. And if the DûnSult are right and the Progenitor's sin was to stray too close to Absolute, then the surrogate soul needs to also be suitably close to the Absolute too.