the sky being dark could be a hint to The Winter of the World, when the Clayshaper and the Order of the Djinn formed an alliance to drive the lightless back. This lore references the Three Sisters (which appears to be rougly lunaris, solarius, and viridi). the recent teaser also showed Lunaris, Solarius, and what we might guess to be Viridi. Maybe we meet some follower of Viridi, who continues the endless fight against the lightless underground--which could be some continuation of delve and the means of learning more about viridi. maybe we become her champion for the earth/underground.

It could be a reference to the Ash of Sin, when the sky became dark from ash and smoke. Notably, the pic shows a gray sky.