The hard part is that as someone mentioned, this is more along the lines of a 'Extension' pack than 'Expansion'. Taking XI as an example, none of the stories were actually tied together, but their own little thing(Otherwise RoZ would have interfered with WoTG IIRC). Therefore, jobs 'introduced' in that area could be accessible through a quest. However, they were still gated in a form or fashion. For example, Samurai and Ninja had been in Kazham. Norg to be exact. However, you needed to obtain Kazham Airship pass before even reaching the quest starter.