My top suggestion would be to make the class armour for the warlock class actually something mystical itself. The Jedi in me would love to see a cloak option as the warlock rose through the ranks. Not a hood. A cloak that would descend and shroud the player when standing still but fly in the wind out behind you on your sparrow. Like a wizard or warlock the hood would be on the shoulder, not over the head thus differentiating the warlock from the Hunter class.