I doubt that they will be using dex as the main stat as it affects ranged damage. It would be pointless imo. There is already a stat that scales properly to include the estimated auto attack damage from melee and that's str. I doubt SE would go out of their way to make that change if they didn't have to. My guess is that Nin will be folded into to the mnk gear set much in the way smn/blm share coil/sold gear.