I've seen on a few additions to pages about the connection between Tharizdun and Cognouza, specifically Kingsley's dream. I feel that said connection is a bit too vague to be recorded properly at this time. Matt's narration of it was very flowery, and coming at the end of nearly 7 hours of gameplay, was winding and somewhat confusing.
The interpretation I've seen is that the "black chain" was one of the chains that bound Tharizdun, and that it was connected to Cognouza. The fact that it was destroyed would mean that Tharizdun is closer to being freed.
I believe this interpretation is false. Most superficially, Matt described the chain as black, and the chains seen in "The Cathedral" were golden. However, the timeline doesn't match up. Aeor was destroyed, and Cognouza shifted to the Astral Plane, early in the Calamity. Tharizdun meanwhile was sealed towards the end of it.
My personal interpretation is that the chain was representing Tharizdun's maddening influence on the Somnovem and the people of Cognouza. The Somnovem were driven insane by a supposed Psychic Wind, and Tharizdun is the god of madness.
Ultimately I think for now the nature of this connection is too vague to be recorded on the wiki, and speculation is best kept off the pages.