In the last 24 hours a Reddit post by user Reidor claims to have discovered evidence suggesting Heartstone: Heroes of Warcraft's next expansion is called Lost Secrets of Un'Goro.
The 'evidence' of this is an alleged CV of voice actress Lani Minella, who has previously worked on Hearthstone before in the Whispers of the Old Gods expansion, if the CV is to be believed.
Who knows whether this is true or not, but it seems to have got plenty of people talking nonetheless, in no small part because Un'Goro is a featured area in World of Warcraft. Does this sounds like a feasible title to you?