So what does this have to do with a possible third class? Quite a bit.

The clincher is the Primals and their followers. Those who have played 1.0 and now A Realm Reborn will notice that while the followers were in 1.0, before they did not use enhancing Enhancing Magic. For those unsure what that means, in Final Fantasy XI enhancing magic was a skill set exclusive to the Red Mage (at least at start) that included Enstone, Enfire, Enaero, Enblizzard, Enwater, and Enthunder which would add elemental damage to the Red Mage's melee attacks.

Taken altogether almost every single spell from the Red Mage's arsenal is now in the game or in the coding and dormant thus the rumour of a possible third class would fully make sense were Red Mage to be introduced as Conjurer, Thaumaturge, and Gladiator (Or Arcanist even though highly unlikely as Red Mage's are sword users).

These are just my observations, feel free to interject any thoughts you might have.