I'm willing to bet that SE will start releasing jobs to branch off current classes and add some more classes later when they add new weapon types. It makes it MUCH easier to do this jobs, rather than having to create a class from scratch every time they want to add a job to the game. In terms of lore, they can easily fit it in; classes can have their own guilds and jobs will be part of that guild.

However, one concern I have is the leveling process. Level 50's can just switch over to the new job after unlocking it without ever practicing with it. I just hope these additional jobs are even harder to get. Like, I hope unlocking Scholar will be a lot harder to unlock and fully master (learn all skills from job quests) than Summoner will be. That way, it can give people time to fool around with the job and get the hang of it.

Just because I want to have a bit of fun with this idea before being hauled off to work, let's try to imagine what kind of jobs we could see get added in the future

Archer > Ranger
Marauder > Berserker
Gladiator > Black Knight
Conjurer >Oracle
Thaumaturge > Geomancer or Blue Mage
Pugilist > Boxer? idklol

New classes to be added:

??? > Red mage and Sage
??? > Thief and Ninja