I'm afraid this will never happen, because of some reasons.
1.: There are to much crying, that classes without job are useless after Lvl 30. The advantage of the jobs is so huge in Endgame so no one wants to sit on a class without Job or they get harrassed for that behavior.
2.: Much Jobs got new job skills, who are primar for other classic FF jobs like the "Deliverance" and skills depending on this would fit more to a berserk or wiking job, Bard got much Ranger like skills.

In conclusion of this (yeah its just two) points it wont happen like you mentioned. Instead of introducing new more powerfull "megajobs" as an upgrade for existing jobs, they will improve the jobs with new skills from classic classes to fit in this spot. And white mage is a sage in the terms of master in healing and damage at the moment, he just isn't called so, cause he can't use classic black magic (fire/ice/lightning).

Perhaps they will do this, and it could work, but the community wants just new jobs in horizontaly not in verticaly progress, so they can acquire them fast and easy.

This is just in my opinion what will happen. I would like a vertical progression in jobs too, but i don't see that comming soon.