What pirate faction, you say? The Bloodsail Buccaneers of Booty Bay have their own limited faction gains and rewards. Killing goblins and doing the few available quests will get you a pirate outfit, but not much else.
Player Bloodysaber of the Uldum server would like to see more. He'd like to see it so much, he wrote up an entire faction design document for Blizzard to follow. This document not only including quests, NPCs and faction rewards, but also new pirate gear with stats, a pirate title and a pirate town in the form of a boat parked off shore with vendors, flight masters, engineer trainers and quest givers.
If you're in the pirate mood today, head over to his thread and give him your support.