Minfilia as a Rouge

[Theodric]

I certainly do hope that if the trust system is a solid success, it gets expanded on and allowed to include other characters beyond the Scions.

I suspect it will. There's a lot of characters that would make for solid additions such as Arenvald, Estinien and Fordola.

Potentially the likes of Hien as well, even if it is only for a dungeon or two as part of the ongoing story.

Antagonists joining for the occasional dungeon would work very nicely too. Vagrant Story had a special fight where that happened and guest characters played a part in quite a few of the Final Fantasy titles.