Someone suggested that I separate my theories blog into separate posts by subject. If you're looking for the blog post with complete theories, it's still here.
Daeonica is mentioned several times in the book, and while we don't get to hear the entire thing, I've been wondering if Daeonica might be a different version of the story of Lanre and the Chandrian (though obviously with different names) which shows Lanre in a more positive light. This is more of a feeling that I have than a fully-flushed out theory, but I think it could fit. Arlidan mentions stories in which Lanre sells his soul (though Ben says that this is nonsense), and we know that in Daeonica Tarsus sells his soul. I think the "hell" mentioned in Daeonica is actually the realm beyond the Doors of Stone. I'm not sure if the revenge that Tarsus says he's bringing down would be on the world that stole Lyra from him, Selitos, or Iax himself. Also, in Wise Man's Fear, when Kvothe is researching the Chandrian, he mentions that the names are easier to come by, but most of them are stolen from the Book of Path or Daeonica.