World of Warcraft is patching in a way to purchase Legendaries directly in patch 7.3.5
One of the most ongoing issues in World of Warcraft’s current expansion has been the preponderance of Legendary items and the general difficulty of acquiring them at all, much less acquiring the one that you need. If your luck is bad enough, you could easily keep striving for one and never wind up with the one that you need, or potentially with any. This arguably counterbalances any and all fun from when one does drop, but it’s finally being addressed in patch 7.3.5 with a new purchasable item that will always drop a random legendary.
The Purified Titan Essence in question requires 175 Wakening Essences, so it doesn’t come cheap, and using it will produce a random Legendary item for your spec. Obviously, that doesn’t mean it will necessarily be an item you want or need, but at least it’s a currency-based means of getting a Legendary item instead of praying for another day that you might get lucky with your emissary chests.