So, it's not an Enantiomorph without a Catalyst, then? The Imperial Simulacrum seems to have a lot of parallels with the Enantiomorph, and although it's not mentioned in the http://www.imperial-library.info/content/rebels-return I can't help but feel that's deliberate. But I can't think of what the Catalyst could be.
We've got the King, Uriel Septim VII. Jagar Tharn is the Rebel, who uses the Staff of Chaos to banish the Emperor and literally become him, taking the place of the King. Ria Silmane takes the role of the Observer; she's the only one who knows of Jagar Tharn's betrayal, and is obliterated by Tharn for knowing. The Prisoner is obviously the Eternal Champion.
It's a bit harder to fit Miraak into these roles, but I like Miraak so let's see if it's possible. http://www.imperial-library.info/content/guardian-and-traitor sets it up: Miraak the Rebel/Traitor fights against Vahlok, the Guardian/King, and is whisked away moments before defeat by Herma-Mora, who represents the Observer (and yet doesn't get maimed as far as we know, but who could tell with an eldritch abomination).
OR. Miraak is actually the Prisoner; Akatosh is the King, Alduin is the Rebel, (who's the Observer?) and Miraak (and then the Last Dragonborn, after Miraak fails) is the "Wild Card", a character unbound by fate who has the potential to tip the scales in the direction that saves the universe. I've http://www.gamesas.com/topic/1505482-could-miraak-have-been-a-hero/ that Miraak could potentially be a Hero who never bothered with his "destiny", similar to the Failed Incarnates of the Nerevarine prophecies. It's worth mentioning that the aforementioned Guardian was named Vahlok the Jailer.