It seems like there's a point at which a consciousness is so powerful, that it can't grasp itself and goes mad/completely unstable and destructive. Or maybe at some point out of its awareness over 100% of it is needed to sustain awareness of itself... and something happens. And it stops being aware, just malignant, unaware of its actions and so powerful it can immediately incorporate other awarenesses into it. This seems paradoxal, but it's also very interesting.
That would totally confirm the phrase "The deepness that stalks the cold roads", not "darkness". Possibly comparable to a black hole, just on a psychical level. Once you get too near it, it sucks you into itself and you simply won't get out no matter what. It would also seem that any psyche that gets sucked in becomes some kind of no-shape blob, just like the matter in a black hole.
It also seems that calling it God or God-like seems to make sense. Since it seems that it's being attracted VERY quickly by any thought about it, which would mean that either it sees everything in the open spaces of Nagari network simultaneously, or there's just some magic summoning it to whoever thought about it. Since witnessing such thing seems to be VERY traumatic, it would also seem that Ken in UT2 actually didn't only place a firewall between Laporte and it, but also actively erased Laporte's memory of it. Because if he didn't, she would almost instantly think of it.
So it seems that Shivan's role is to remove any single entity that's even remotely close to becoming such a thing, while Vishnans seem to convert entities they seem fit into parts of the Great Psyche, which is either separated from the rest of Nagari... somehow, or whatever is in the Psyche isn't aware at all.
It also seems very paradoxal that human awareness was developing quite slowly if at all, and the actual reason for it to be able to reach Nagari or whatever's in it were the Shivans themselves. The research about Nagari became because of them. So if their goal is to prevent civilisation from reaching an awareness threshold, they seem to be doing it very wrong by providing tools like Nagari for the humanity. I think that's Vishnu's idea.