Branching jobs from a single class were a nightmare to balance and make correctly, it's the only class to ever do it and will stay that way. They said they didn't like the way the design was for developing skills for, etc. As far as general classes branching out into a job, that's dead too, they just tend to release the new jobs as stand alone without the hassle of having a class attached to it.

Elementalist is an interesting concept but they already failed on the elemental damage aspect of this game, hence why all the skills do unspecified type of damage. BLM was pretty much an elementalist to begin with but they scrapped that idea long ago.

DNC was DPS in XI with some heals and could tank with NIN or WAR sub but again this isn't XI and DNC is kinda iffy as much as I and others want it.

Devout Healer, we already have an AST which is basically the same concept, just different lore.

They also tend to not make up jobs on the spot, the exception is AST if I recall, everything else will more likely be pulled from existing jobs in previous games, until they run out of those said jobs.