Trailer safety spoils.
The fact that they opted to show off Zodiark in the trailer is really making me further doubt that he's going to be the climax of the story and it would not surprise me at all if Zenos does succeed in controlling him, but simply serves as the second trial boss of the MSQ.
From reviewing the past expansion trailers, they're not shy about showing off basically every instance/zone other then the final boss, so I'm wondering whether that winding path of crystal or that barren land of death is going serve as the penultimate dungeon before the real final boss.
Though for all we know the latter might actually be the final zone now that they revealed the Scions will actually tag along with you for certain MSQs out in the field as opposed to simply teleporting off to where they're supposed to be.