Silvereye Sliver

I know I'm a bit late on this discussion, but I just had a thought after reading the Secret History. *spoilers for both Secret History and Bands of Mourning.* The people at IRE fort seemed afraid that shades from Threnody would be invading their fortress, which they believe would have occurred to get in on the opportunity ascend as a shard bearer on Scadrial. In Bands of Mourning, the Set work with a group of beings who have a metal that Harmony is not familiar with and Edwarn states that they have faceless immortals of their own. At the end of the book, he is visited by a being with red eyes that states that Edward will serve him in another realm and that life will be wiped from the planet. Immediately afterwards, the being blows him up in the physical realm. Now, the shades from Threnody have red eyes and like to create more cognitive shadows like themselves. What do you think are the chances that the red eyed beings are shades and the Trelagism religion is a front for an invasion from Threnody?

Another point of interest is that the letter writer states that: "Let me first assure you that the element is quite safe. I have found a good home for it. I protect its safety like I protect my own skin, you might say." Brandon has confirmed that Hoid has a nugget of Lerasium, the godmetal of Preservation. This could be the element mentioned above, which would add further evidence to the theory of Hoid being the author of the Letter.