I'd LOVE if we had a caster tank like Red or Blue Mage. In the first case, you could use defensive spells like Blink, Phalanx, etc. And in the second, you could use Cocoon, Metallic Body, etc. (true there are no mobs in the game with those abilities currently but that needn't limit SE from doing something like this - give BLU those abilities anyway or just make new mobs with those abilities).

RDM/BLU could cross-class Protect, Cure, Stoneskin etc. RDM could also have a few enfeebles (Dia, Paralyze, etc.) and other misc. enhancements (En-spells, Refresh). I'm not sure what direction you'd want to take BLU with this game though. But the possibilities are exciting. All I know is I've put everything into leveling and gearing WAR but I'd trade all that for the chance to tank w/ RDM (maybe BLU).

Back to the whole Samurai thing though. I hope they're DPS. If SE ever adds Ninja, I think they should make them an evasion tank like in FFXI, although they'll most likely make them DPS. At least either would make sense. I just don't buy the idea of Samurai as a tank. It doesn't feel right to me.