It looks like the next Hearthstone release will be centered around the lost world of the Un'Goro Crater. An entry on the resume of veteran voice actress Lani Minella shows work done on "Hearthstone: Lost Secrets of Un'Goro". The resume is hosted on Minella's own site, AudioGodz, and was first noticed by the internet sleuths on Reddit.
Minella has previously worked on Hearthstone, offering the voices for Cult Master, Arathi Weaponsmith, and Imp Master in the first release and Faceless Summoner, Twilight Geomancer, Ancient Shieldbearer, and Darkshire Librarian in the Whispers of the Old Gods expansion.
This assumes Lost Secrets of Un'Goro is the next release for Hearthstone. Given the tick-tock release schedule for Hearthstone's Expansions and Adventures, that would make Lost Secrets an Adventure. Blizzard Entertainment recently released the Mean Streets of Gadgetzan expansion in December 2016. Gadgetzan is located in the Tanaris Desert in World of Warcraft, just east of the Un'Goro Crater where Lost Secrets would take place.
Hearthstone game director Ben Brode recently made a huge post on the official forums promising huge changes, tweaks, and shifts in the game's current meta. The post outlined why Blizzard has yet to address the strong Shaman decks and offered upcoming nerfs to certain Pirate cards used in many top-level decks. He said that balance changes were coming to Hearthstone at the end of this month.
"Our next patch is planned for around the end of this month. You can expect an announcement from us regarding balance changes either way in the week or so leading up to that date," said Brode in the post.