While, for now, Garlemald may be content with its situation on Azys Lla, having de facto dominion, or at least claims, over it but with an entire legion stranded there, it may well be that, at some future point, some successor to Regula could finally be appointed as either the legatus of the 6th Legion or the viceroy of Azys Lla (likely to both positions) and have their sights set on Tiamat, and troubling the peace between man and dragon. However, I don't have more ideas for how to make such a storyline work beyond these two arcs:

1) The Gration (a dungeon): you pose as some Garlean dignitary, ostensibly for inspecting damage to the ship, in an attempt to destroy the Gration and make it look like a mutiny

2) The Aetherochemical Research Facility (hard): cornered, the viceroy of Azys Lla makes a last stand at the ARF and is fought as a last boss. (I would prefer the resulting dungeon to be harder than the ARF normal)

The viceroy of Azys Lla could be a relative of another Garlean character but beyond that, give it some redeeming quality. Maybe the viceroy could be appointed there as a trial of fire for the highest echelons of Garlean government, or as a last chance for an official who's falling out of favor.