Since it's possible to travel through the void (via portals), and we always see a faint grid when we look into void, it's reasonable to assume the lines on the grid are connections between portals: we never saw any connections to or from Cleared DL2 except our own Checkpoint, and the void there was dark. Notice, too, how the lights in the void are always on the grid lines. Combined with the knowledge that Soul Stars are broken as people fall into the Warrens, we can infer that each light is a Soul Star in the process of splitting, stolen from its owner as they travel to a Dungeon Level or elsewhere.
Though javierpwn got the bulk of this answer right, monk12 wins alongside him on a technicality. PoV characters are controlled by the players who are represented by the ghosts (memories?) of dead adventurers, dragons, etc. The PoV ghosts are all who have entered the Warrens and died. Since the number of these ghosts is increasing - Ciro even saw this happen - this must mean the number of suggesters/readers is going up, and it always is! The lights in the void are us, though not for the exact reasons monk12 said.
In other words, every time someone starts playing TWoOtA, some random fictional character has their soul eaten.
So, we should each be present in the warrens, as "ghosts" of one sort or another.
Slog reconnects with the remnants of his soul, re-gaining consciousness (or the Slime equivalent). The Essence of Slime disappears.
This statement implies that essences contain a souls' consciousness, memories, and basically everything else needed for the soul to achieve some semblance of functionality. This implication is further supported when we see the sheer blankness of soul star bindings. Since our minds are (mostly) functional, we can assume that whatever state we're actually in, we have access to our essences, if not our entire souls.
Since essences contain not only a person's consciousness, but their memories as well, logic states that each reader of TWoOtA is wired to an exposition dump.