As far as I know, SE plans on adding additional jobs to the current classes. The big issue I see is that each class is very rooted into a core rotation that is minimally affected by its job. The multiple jobs worked well with arcanist because the class was designed from the start to support two seperate roles, but not every class seems to be built in such a way that different jobs would create different playstyles. The root of the issue is that there are only 5 job specific skills, most of which are situational or passive.

Take Pugalist/Monk as an example. The entire class is built around moving through its 3 forms with its 6 primary attack moves, all of which but one are pugalist skills. No matter what they do with the 5 skills there can't be much of a difference in play-style because it is so closely tied to its core rotation.

The same can be said of lancer/Dragoon, and I'm sure most other classes.

This is on top of issues such as instantly being level capped with a job as soon as it comes out because you already leveled its base class, creates more RNG on bosses that drop job specific gear, and stat allocation being tied to the class instead of the job.