I think the idea that SE makes (even if mini) a new expansion that has stories of the original of each class. Make it that it really immerses the player into a long since forgotten story for each class but make it you have to fight every fight as that class.
You could also have it that all stories converge at some point for large fights for added story feature on all sides.
For example: Smn story.
You learn all about the avatar's on a more personal level and about the quest of a brave adventurer in their quest to quell their anger and starting bonds with them to the point that they become an summon.
At the end of the missions which ever story line you choose you get an item that when traded to your hero's forgotten grave with your original artifact weapon gives you a new weapon that is catered to your current jobs abilities/skills.
I know it would take a lot to program all of this for each job but i won't complain if you recycle old area's again. i just want a new story to follow.