At this point, I'm very much expecting a third party entity to ultimately be to blame for the entire predicament. Potentially the very same entity that caused the Sound. The writers have, thankfully, been pretty clear at establishing the nuance of the situation. Neither Zodiark or Hydaelyn are necessarily 'good' or 'evil'. It's all very much a matter of perspective. So, too, does that apply to the Ancients and the Ascians, the Sundered and the Unsundered. They all have their own goals, dreams, desires and a will to live.

I also suspect that the Warrior of Light will go the way of Azem and seek to find a 'third way' when it comes to solving the plight that is the Sound. Especially if the Final Days are indeed returning for a second time in the same form as before. Or, alternatively, perhaps the story will involve Hydaelyn and Zodiark being brought together in a state of balance - given that the Sundering has been described as an 'unstable state' by the writers themselves in the past.

Whether Venat is an antagonist or not, I suppose, depends entirely on a few key factors such as whether the Sundering was accidental or intentional.

My own personal hope is for the story to set aside differences, acknowledge each side as having understandable motivations and then have everyone come together to beat the Sound which may or may not be a Lavos or Jenova type entity in typical JRPG fashion.