One possible idea with the remaking of the world would be guilds for new classes set up by people who have come across the sea top help rebuild the world. Limsa is a seafaring nation and it seems plausible that maybe a foreign sailor or passenger could bring the new knowledge with them. New lore could also be found in the wreckage once the moon lands, it is after all artificial. Or the crash could unearth ancient ruins with scrolls allowing the re-emergance of forgotten skills. There are a thousand ways to introduce new jobs which don't require an expansion zone.