Perhaps the Heart of Sabik is Unukalhai from a parallel world? Or maybe even Unukalhai is what's left of Sabik after he lost his heart?

I also feel it's worth mentioning that everything in the cutscene direction points to Eldibus being our enemy at this point, so the twist Moose wants is more of an untwist. He's just spent way too much time around those of us reading ahead that he thinks there's actual evidence of him being on our side at this point. Alas, there very carefully isn't.