A new easter egg with the Arsenal: Cosmic Weapons Cache rewards from the November/23 Trading Post has been discovered! Thanks to Twitter user Korrin for the tip.
The Twilight Hermit is a NPC that was originally added to the game in Battle for Azeroth. The Hermit was already shrouded in mystery back then, as he was the person you would bring the Wriggling Mass you collected during your Island Expeditions.
In the quest Wriggling Mass, you would learn that holding the mass would plague you with visions, and by turning it in to the Hermit, you would learn he used to be plagued by the same visions — until the day Sargeras struck Silithus.
Back then, this was simply a hint about the Old Gods and what followed at the end of Battle for Azeroth. However, new developments with this NPC shows interesting dialogue for what the future might hold!
The Arsenal: Cosmic Weapons Cache was the Traveler's Log reward for the Trading Post in November/23, and contains 5 weapons: