I truly feel that Samurai if introduced would come from Doma. If this were the case, it would only makes sense that they would be Tanks as we already see the Ninja is a DPS. To believe that such a large majority of the Doman military force were only suited to only one role seems not only awkward, but also feels uninspired. Furthermore as we already have Monk as a DPS aswell, the eastern themed DPS niche seems to be well covered. I do feel sword DPS should be implemented however and would enjoy seeing some iteration of a dual wielder sword class/ job introduced. I feel Red Mage and or Blue Mage would fit the bill quite nicely. In looking at the way Astrologian was introduced, it's not out of the question that we may already be seeing new classes in the game. Ala Mhigan Shamans and Sword Dancers already exist in some fates aswell as there being supported lore about Lancers.

In short I feel sometime in the series we may see Samurai as a Tank before the next expansion. Perhaps a lead up to 4.0 addressing Ala Mhigo where we may see:

Lancer = Templar (Lance and Shield) Tank

Blade Dancer = Red/ Blue Mage (Dual Swords) DPS

Shaman = Geomancer (Axe/ Mace and Shield, Dual Axe,/ Mace, Two handed Hammer) >.> Melee Healer... Yes alot like that other game...