Hopefully Insomnia too.(maybe even Post game.)
God, they don't even need to make it into a full fledged, living breathing city. If they just turned it into the largest exploreable dungeon ever where you can explore most of the city and just fight high level daemons all day or secret bosses, I'd gladly pay tons of money for it. The entire city is already fully rendered, just make a separate map for it and throw us in there with some content! If they did it with Gralea as well, but instead of Daemons, it was even higher leveled Magitek Army enemies, I'd die of happiness.
Seriously, thats how you make these 2 cities open to explore, just "endless" dungeons with some points of interests sprinkled around the map. Salivating (and crying) just thinking about it.