After reading the preview of SAS Part 1 and the transcript of it, I have some theories on the spirits that appeared before Ukano who, before today, had only the name "Mai's father". It could actually be Ozai, Azula, hallucinations of Ukano, Zhao, the spirits of Azulon and Sozin, etc. The Kemurikage spirit "fable" could also have a link to Mai and her childhood.
Preview: http://terrible-wander.tumblr.com/post/113129667389/smoke-and-shadow-part-1-preview