If they were going to release a new skill, it should be something cool, entertaining, that everyone can do (F2P and P2P) and can be trained in many places. Dungeoneering was bullshit.
@"ReloadedPK", I think that your agility should increase while you run.
I'd like to see them add some form of PvP with sailing. You could get a bunch of friends on a boat, then you could use cannons to shoot other peoples ships with different level cannons and cannonballs, I.E. Rune Cannon, Dragon Cannonball. Then you'd board the enemy's ship and kill them from the deck. Piracy.