6.0 Story Speculations

[Enkidoh]

I have to say it’s interesting to see people think Zodiark will still be the final boss of the arc despite the trailer depicting us as a paladin on the moon...almost like we’re protecting it, while the source glows a dangerous hydaelyn blue...

That's just a deliberate FFIV reference where Cecil (who like our old friend Derplander went from DRK to PLD) ends up on the moon as well at the end of the game (and which is where FFIV's final bosses are fought too), it's nothing to do with "protecting the moon" - we're on the moon to destroy Zodiark for good, even SE themselves hint that pretty hard on the main EW site:

Take heart in the faith of those who walk beside you, and journey ever higher─to the very stars above.

and

Journey to Thavnair, the imperial capital of Garlemald, and even the moon!

Of course they don't say that "Zodiark is the final boss", but as the moon is Zodiark's literal prison, and the aforementioned FFIV references, it's pretty clear that's who we will ultimately be facing at the finale, and where.