Evidence has surfed that the next Hearthstone card drop (be it in the form of an adventure or a full-blown expansion) will be taking us to Un’goro.
A sleuthy sleuth on reddit found mention of “Hearthstone: Lost Secrets of Un’Goro” in a voice actresses’s resume.
The actress in question, Lani Minella, has done voice work in Hearthstone before (Cult Master, Imp Master, Arathi Weapon Smith) so there seems to be enough credence to this leak to believe that it’s probably true.
And since Blizzard typically rotates between expansions and adventures, and since they last released an expansion, (Mean Streets of Gadgetzan) I’d wager that Lost Secrets of Un’Goro will be an adventure.
No telling when exactly it’ll release, but once Hearthstone’s next year begins (when they rotate out older card sets) is a good bet.