Ninja seems like a dex character seeing as we already have 2 str classes and dual wielding daggers/short blades requires more dexterity and finesse than actual strength. I highly doubt that SE will Ninja have double stacking stats. All the current jobs only require to put all 30 into one stat be it vit for tanks, str for drg, etc.

I think SE missed an opportunity to make classes more diverse by not giving us multiple stat stacking but that would be hard to balance and we all know how important in-game balance is to them.