How can they add more classes and make them unique and have their own flavor?

[RiceisNice]

I remember I read somewhere that Yoshi P said that they will add more jobs instead of giving jobs more specializations (IE DPS Paladin, Heal Paladin).

The primary reason they can't do this is because even if you try to change the role of a job, it doesn't change the fact that they're drawing from the same level 1-50 class abilties, which is hwere the foundation of their gameplay is built upon. Take a DPSing SCH and SMN for example, back in 2.x they shared identical dps rotations minus fester (in which case they'd just use energy drain instead). Even if you had put a dps warrior, they'd still have the same BB and maim combos, not to mention deliverance makes it sort of a redundant concept.

The same way dark Knight, ast, machinist and ninja feel unique compared to the other jobs in their role

My sides.

But on a serious note though, they just have to take the idea and run with it, not play it safe. If a job ends being undertuned or overpowered numerically, you can always adjust the numbers. Mechanics on the other hand you can't really cut corners around (much like how they scrapped the idea of attachments and ammunition on MCH). You have unused concepts like a swinging TP resource, spellblade, stance dancing for dps (not tank/healing), or even a stationary melee that moves with abilities.