About the Eyes and ideas floating around about them...
I'm fairly confident the close-up on Nidhogg's inert Eyes as we tossed them off of the Steps of Faith was meant as a visual cue that "the Dragonsong War is over, and its perpetuator gone forever." We tossed the Eyes from so high up we can't even see the bottom; while I can't say anything about how damaged or otherwise they may be (given Estinien gouged Hraesvelgr's loaned Eye out of Nidhogg's socket, then its owner put it back in half an hour later and was totes fine), the chasm seems nearly bottomless. They're probably beyond the reach of any mortal, at least... but back to the point. They're gone from the narrative, probably forever, and Nidhogg's spirit departed before we threw them, so even if someone did get them both, he's gone. Probably definitely. So there will be no Nidhogg-possessed rats coming up to menace Ishgard.
So too is any plot thread dangling from said Eyes. Probably. So Lahabrea is gone for good. Probably. And the "but he could still be alive in the Eye!" argument is now a moot point because regardless of whether or not he is, the Eye(s) are gone. Probably.
As for Blanhaerz' observation, he didn't seem to be acting at all - just observing, as the Warriors of Darkness have been shown doing aside from their scuffle with Ravana and us. I can't check if he was looking down before / while making his call because of maintenance, but right now I'm going to put my gil on him looking down to make sure we threw the Eyes off of the Steps... according to plan. Nothing about retrieving them, just making sure things are playing out according to Elidibus' script. (In fact, Lahabrea getting offed was probably beneficial to Elidibus' plan, since a chaotic element like him isn't conducive to a complex scheme like Elidibus seems to be setting up.)
As an aside, I'm now looking forward to being that chaotic element that destroys Elidibus' well-orchestrated plot.
As for Omega, it was mentioned what, once, back in 2.3? I'm not betting on it showing up again until someone says something about it, and besides, it's still a scrap heap buried in Cartenau as far as we know. Unless someone excavates it and gets a master machinist to refurbish the thing, plus a nice aether / ceruleum supply to fuel it, it's still useless... and that's a lot of conditionals. It's certainly beyond the means of Ilberd.
You know, Unukalhai's exposition on Auracite reminds me a lot of VI Magicite upon further thought... makes sense with the Triad as a backdrop... but anyway.
The idea that our use of Auracite will corrupt us over time, and thus that we should stop using it, seems baseless. We only use Auracite to trap an Ascian before blowing them to smithereens; Unukalhai's story exposits that people held onto the Auracite with a trapped Primal so they could use it for power / war. Besides, Moenbryda outright stated that the White Auracite we use can't hold aether for very long - not exactly what happened in the story. Whatever sort of Auracite the people from Unukalhai's story were using, it certainly wasn't the White kind we use. (There are other kinds of Auracite?! This is also news!)