1) A letter dating before the First Blight mentions concern that the lack of communication with Heidrun Thaig might be due to "those creatures that wear the faces of the dead".
2) In the Chronicles of a Forgotten War series, the Scaled Ones (possibly Helsdim's Snake Men of the Earth) gather the corpses of dwarves, using their gray, drained husks in some kind of blood/flame-based rite or religious ritual, the result of which is never discovered.
3) Post-Descent, Inquisition scouts discover that Lieutenant Renn's grave "was recently disturbed, and his remains are missing".
I don't know how much we're intended to connect, but taken together, these three are unsettling. Given Valta's post-end codex describing the domed pool of lyrium and the sets of empty armor, I don't think this is directly related to the Sha-Brytol... but if not, what's the connection?
Also, is it a little weird that we've never seen darkspawn versions of these Scaled Ones? Being a few days north of Cad'halash isn't out of blight range by a long shot, particularly since they seem to have been underground to begin with... though I think the Forgotten War codex has to be predate the first blight. (Right? Cad'halash exists = Arlathan hasn't fallen = pre-rise of Tevinter = pre-Blight?) Which leaves any number of possible explanations, from natural immunity to obliteration of the race before darkspawn contact.
Yet another dangling lore thread. TwT This DLC is killing me.