Really, I'd just like to see GCs or some analog in each city that you can unlock as you progress the story. Ishgard could be the Temple Knights, Crystarium the Guard, Radz-at-han the Radiant Host. There's not a whole lot of strong lore reasons they couldn't do the "Adventurer Division" thing the GCs are doing once you reach certain points in the story. In fact, for the Temple Knights and Crystarium Guard (especially the Guard), it fits right in line with the story and thematic elements present.

GCs as a feature have just been abandoned, which is a bit of a shame.