(Source: Legion Summit Dev Interview, Video | Text Summary) the chances of you getting a legendary will slowly increase if you don't have one drop).
UPDATE: The latest Beta patch has adjusted many of the passive effects of these legendaries. It shares a model with Crown of the Forest Lord, a Leather helm that drops from Swamplord Musel'ek, the third boss in The Underbog, a level 70 dungeon in Outland. Comment by jjanchanThis helm bears a set of antlers on it.