I had a new line of thought. The Great Darkness may be a sort of vacuum, which feeds on reality or existence itself, through subspace. Subspace may be like a conduit for anything beyond the physical realm, a platform to browse through with Nagari, like cyberspace, where all realities can meet.
The Great Darkness may have existed before the Brahmans themselves. Rather than having created the Great Darkness, the Brahmans may have filled the vacuum of the Great Darkness, so it does not continue devour. But like all things born, the Brahmans eventually died and they created the Vishnans to find species which could replace Brahmans. Still, the Brahmans made one fatal mistake: the Vishnans were created and therefor they can also die.
Something that can die, is inherently afraid to die and the Vishnans are breaking away from their purpose to try and survive themselves. Maybe humanity is in their eyes a temporary stopgap which delays the inevitable, the Vishnans death. Perhaps the Sync joke in the Universal Truth mission actually is a metaphore for a sink-plug that is plugged into the Great Darkness, a vacuum.
The Shivans may want humanity to take the Vishnans place. If we have shown them one thing, it is that we're not afraid of dying and we do not try to outrun death. We faced the Shivans head on, against all odds. If the Vishnans have started to deceive the Shivans out of fear of the Great Darkness, then humankind is a more solid choice as future wallkeepers. Aken Bosch's deal with the Shivans might be that we'll replace the Vishnans and do a better job at whatever they do. There's no place in that for Vasudans as they are far too prone to resign to fate.
As the Shivans always existed and are eternal, they cannot die. They do not experience fear as the Vishnans might and therefor do not act in desperation. We have been shown they take their time and that they can obivously afford to do so. That inherently does not give them a basis to be 'evil' or 'wrongdoers', unlike the Vishnans who CAN die and grow desperate. They are far less prone to betray us, unlike the Vishnans would.
On a funny note, if Dreamscape is like the internet, does that make the Nagari network something of a deep web?
