A lot of people seem to be going in this direction and want this to be true - to a degree that some of them claim it's the only obvious answer and should be preemptively considered fact. I definitely see it as one possibility, but I see others, and no way we can possibly tell. It's an event without precedent. Though if it was true, I'd have so many extra follow-up questions:
We saw all 14 Overlords in the same place at the same time, both before Solus was confirmed dead (he died this in-game year, five years from the Calamity) and while Solus was "resting." So if he's an overlord, that's strange behavior. And if he's not, who is he? Some up-jumped black-mask? We've never seen a sub-overlord come to our world from another, and we've never seen a sup-black-mask that can leave our corporeal world. And black-masks are ex-mortals, so why is it more likely or more cool that some other ex-mortal transcended and possessed the mortal Solus than that mortal Solus himself transcended? So many questions.
Just because of that, I'm hesitating from moving beyond, "What if it's just the Sahagin elder thing again? A Source-born mortal who got tangled up with the Ascians, transcended the flesh, and is being considered for taking up Lahabrea's fallen post?" Nabriales drew the line between Transmigrationist (often translated as "Reincarnated", but I'm using the less specific version of it) and Original as being "not from this world, or from this world", and Elidibus would want someone local for Lahabrea's station, no?
I saw this same oddity on FFWiki today. Most of this is correct; Varis found out about the Empire's connections to Ascians much more recently than his rise to the throne. In 4.0, when Elidibus first comes to him as Zenos, he's not really clear on the difference between Elidibus and his black-robed brethren and is mulling over whatever this "Rejoining" thing is. He goes along with what Elidibus says, step by step, but often expresses concerns, which Elidibus allays with "Don't you want to save the star?" every time.
But how do we get from there to "Varis wanted the peace treaty with Doma"? The entire Doman peace plan was a farce orchestrated by Elidibus. Asahi shows up claiming that Varis personally promoted him to ambassador and sent him to Doma to treat for peace, knowing full well that this was a lie and believing he was following Zenos's orders. Why would anything else Asahi said be true? Elidibus was trying to use a loyal puppet to make it look like the Populares were given a chance to do things there way and got rekt by a primal summoned by treacherous savages. It was a carefully calculated move to fan the flames of war in a larger plot in which Elidibus promised Varis Garlemald would be able to conquer the world, and the only thing Varis had to say about it was, "I said no eikons." to which Elidibus replied "Don't you want to save the star?" and he shut his mouth. Kind of a big assumption to make, no? I see it as a moment of weakness before he found some measure of resolve in 4.4. Though perhaps he did secretly want the Ascians to botch it, but the idea that Elidibus backstabbed a legitimate peace offer feels like a big stretch.
