That ship has already sailed I'm afraid (pun intentional). There are already two 'pirate' classes in the game, MRD (their lore is that the class had it's origins with Eorzean pirates who actually prefer the visceral feel of a great axe in battle), and the never implemented Musketeer class (MSK) for short, although npcs like Merlwyb have this class (for players MCH basically took MSK and gave it a turret and a fancy way of forming bullets). MCH basically replaced MSK as a result.

So I don't see this happening I'm afraid as it's superflorous.