I don't think it's a coincidence that the voice started speaking the moment that the Eorzean Alliance agreed to go along with Thancred's plan. Nor do I feel like it's a coincidence that the voice first showed up after Y'shtola was fiddling with the relic in the Steppes.

I'm still very much of the firm belief that the story is going in a direction where both Zodiark and Hydaelyn will need to be subdued somehow. Their struggle is, perhaps, a selfish one - with mortals as their pawns. They are, ultimately, two parts of the same being. One cannot exist without the other, so Hydaelyn banishing Zodiark may have actually been a major mistake. That's even assuming she's telling the truth. It seems strange to me that she was supposedly the 'weaker' of the two yet managed to create different worlds and banish Zodiark in the process.

That alone wouldn't make me doubt her, but the way in which she took over Minfilia combined with what happened to Arbert's world makes me wary. Simply destroying the Ascians does not appear to be wise. Yet it's not necessarily a case of not defeating them...it's a case of ensuring that there's both 'Light' and 'Dark' in equal measure.

Perhaps by putting the reigns of man's future into man's own hands, as a certain someone desires...