I think the Duncan/Akka comparison is much stronger than Siona/Mimara. Siona was related to Duncan and was bred specifically to end Letto II's reign. She also had a power that made her immune prescience. Unless Mimara is Akka's daughter (i really hope not) and TJE somehow destroys Kellhus's ability to see her in his thousandfold thought, then I don't see it.
Too soon to tell. More information needed.