There's only one class I would love to see added to the game: Blue Mage. I want a class so genuinely different to everything else we've got so far that it literally stands in its own style.

Instead of being granted skills simply from levelling, you would go out into the wilderness to do battle and learn the skills from your opponents. Skills to heal, skills to harm, skills to protect. It could be the first true hybrid class, able to fill multiple roles rather than being a plain DPS or Healer.