Listen. The next available class is Ninja. Beyond that we DO NOT KNOW WHATS COMING. Very simple. You can speculate all you want. Clues would lead to an engineer/musketeer class but people thought that upon release and they blind sided them with a Ninja. ANYTHING AND EVERYTHING is possible. Ten years from now I bet they'll have 10 new classes, one which could possibly or not possibly be a blue mage. There is no way to know what's coming no matter how much you love a class, that has no impact on what they bring to the game.