I honestly don't think we're done with Zodiark yet.

The fact that his character design in the trial shows him as incomplete - he's only been rejoined seven times - is a big clue that the other sundered bits of Zodiark are still out there.

We know from the 6.1 ending that Golbez is making a debut as a villain. What it he's one of the sundered shards of Zodiark?

Endwalker was only supposed to be the end of the Zodiark/Hydalaen saga. But if there are still remaining bits of Zodiark we need to defeat to return the lost souls of the Ancients to the Aetherial Sea, well, that's a new plot thread to follow.