I don't think FFXIV has alot to fear from the Diablo or even the Warcraft RPG competition specifically.... at this point it's pretty much destined to turn into another niche XI-esque title (to the misfortune of many people who bought the game expecting otherwise ).

However, this is a HUGE year for gaming in general with several excellent titles (i.e. everything besides maybe SWToR) being released. It will definitely keep new people from wanting to join this game in particular.