If you explore near Ash Mountain in Stonefalls, you might come across a sealed door to a cave labeled Apocrypha's Gate. Its been there since launch.

Outside of it, there is a book labeled
Last Words of a Devotee on top of the rocks. It reads:

I won't live to write again. The Dagonites have broken into the inner sanctum. Our escape has been cut off.
They will burn the flesh from my bones, but I am at peace. My thoughts go to Hermaeus Mora. They will be recorded in the eternal libraries.
I go to join the Golden Eye in Apocrypha.
From the note we can surmise a bunch of Mora cultists got ambushed by Dagon cultists inside, so maybe the dungeon could be about retaking the Temple from the Dagonites. With the dialogue Mel Adrys had in Greymoor, it looks like we could go to the Indoril city of Necrom and revisit the lands of Morrowind. At least one of the dungeons has gotta be in Morrowind, especially Stonefalls since it still never got a DLC dungeon like Deshaan did. Given the Dagonites were the main bad guys in Blackwood, if they revisit it they could also connect to the Daedric powers fighting each other and possible foreshadowing to Meridia. Hermaeus Mora is largely untouched as an eso antagonist outside of Dominion/Craglorn quests, so I think they could explore him more.
This would also give us a chance to see Daedra like Lurkers and seekers again, along with this crazy concept art from
Dragonborn made in 2012 of a massive Apocryphal creature:

Would be great to see what happens
my wife left me