(Be aware, while this is talking about a scene from Shadowbringers' patches, it's largely in context of information from Endwalker's patches, so spoiler warning on that.)
Taking the information we have now that Venat's group of Ancients became who we'd know as The Twelve, I had a thought to review the recording of that group in Anamnesis Anyder. While they're all physically in the scene, only three characters speak: Venat, The Watcher (called 'Diplomatic Ancient One' in the scene)...
And this one.
They actually do a pretty important job of setting the scene around the meeting, this isn't just some do-nothing NPC. For reference, their full textbox (and immediate surrounding dialog just for context):
So not only are they the one that tells us that the Convocation aren't listening, they're also apparently the one that brings the news that Azem's not answering. And this is one of the Twelve.Diplomatic Ancient One: By the summoning of Zodiark have we been granted a reprieve. Yet immutable as the laws He has woven may seem, they will not serve to forestall our doom.
Distressed Ancient One: Nay. Should we continue down this path, our fate will be the same.
I said as much to the Convocation, of course, but the stubborn fools turned a deaf ear to my warnings.
I had hoped that the defector, at least, would side with us, but I regret to report our overtures have gone unanswered.
Whither tend your thoughts, Venat? Where you lead, we will follow.
Venat: I shall not speak ill of the Convocation─they too seek only to secure the future of our star.
So... who is it?
A few thoughts from both my own musings and what other people have said when I put it forward:
+Thaliak, being the headmaster of Akadaemia, has both the position and skillset to be able to give a statement to the Convocation even if they're being stubborn... and is also the type to call them 'stubborn fools'.
+Halone, being in the running for the seat of Pashtarot, might be able to tweak a few ears and also has that sort of vocabulary.
+If anyone's going to be hearing from Azem besides Venat, it's probably Azeyma.
+It sounds frustrated enough to be Byregot, who's probably also of a position high enough to get a word in.
-It sounds too rude to be Menphina or Nophica.
-It sounds too nice to be Llymlaen.
Those are all ultimately my vibes, though, and I might be reading the tone of both those lines and the surrounding situation very differently to others.