I feel there's potential that hasn't been tapped into yet with the passives we have seen on classes. Most of them are just duration or number buffs. What I like about passives is their potential of changing the way the job is played, and these passives usually have the most repercusions on how you play your Job and think about your rotations.

I'm hoping we can see more passives like Thundercloud or Firestarter, which actually change up BLM's rotations and how the job is played, and less of the boring duration/cooldown buffs that are incredibly boring and leaves much to be desired.

With that said, this potential can be tapped into with the possible additions of Job passives, I find it weird that the Job upgrade doesn't have passives that further differentiate how the Job is played and make it more unique. I really hope we see these in the future, because I really think Jobs need a bit more dynamic play to enhance the fun of playing it. Stuff like "Overcure" is pretty cool, but any passive in, say, Marauder is stupidly boring and uninspired.

TL;DR: I feel passives usually have the most potential to change the dynamics of how a Job is played and enhances the depth of play, as of now, most passives seem dull and uninspired and we could see improvement in dynamic play with better passives and possibly additions via Job Passives to make our Job advancement more unique and meaningful.