I'm almost 99.99% positive this will never happen. For starters, DEX is clearly outlined as increased ranged attack power. So, unless they entirely revamp the way stats work for a single job, this will never happen. It'd also be pointless to have DEX increase their physical attack, seeing as that's what Strength does already. It'd be two stats doing the same exact thing.
Second, it's been shown that they're going back and adding in equipment for ninja in past content. We've seen concept art of the Leviathan Dagger and for the Coil 2 Dagger. In line with this, we can assume they are going to be making some sort of armor available to Ninja from Coil 2. As opposed to making an entirely new set and further spreading out the loot tables for endgame content, I can almost guarantee you they will stack Ninja on top of another job's gearing, much like how Black Mage and Summoner share their equipment.
It's going to be Monk and Ninja, and I'll give you three solid reasons as to why that might be. One, they're both martial arts. Historically, martial arts based classes have more or less shared gear, like in FFXI. Two, Monk wears more balanced armor than Dragoon. Dragoon is considered "heavy" for melee, and their equipment's defensive bonuses reflect this. While Monk has a lower physical defense, it's magic defense is balanced with it. Dragoon, on the other hand, has a much higher physical defense, and a lower magical defense. It'd only make sense for Ninja to be wearing the "lighter" class of armor, given it's agile nature.
Last, but not least, we have the Fuma set. In line with what I mentioned earlier, SE has shown that they're working on gear for Ninja in previous content. You would imagine they would want to add a set of gear for them in the Labyrinth of the Ancients, right? Give Ninjas a reason to do the first portion?
Remember what everyone said this armor looked like when it first came out?
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