Blizzard has said that Warcraft 4 isn't on its current docket, saying fans shouldn't get too excited.
The Warcraft brand has been taken over by the visage of World of Warcraft for nearly 15 years now. (If you don't count Hearthstone.) It's understandable too. WoW is one of the biggest games ever released. It has a tail like no other out there and remains at the forefront of gaming still. It's obviously a place Blizzard is putting all it Warcraft stock and I don't expect that to change. Despite having mixed reactions right now, the latest expansion, Battle for Azeroth, sold very well.
That being the case, there are still strategy game fans who want to see another game in the genre the franchise was born in. With Warcraft 3: Reforged on the way, players are looking back to the real-time strategy roots. Of course, that brings up the question, could a new game with a new story come? I wouldn't get your hopes up. Talking to Gamespot, Blizzard senior producer Pete Stilwell said that there aren't currently any plans for a Warcraft 4. He said:
I mean, I wouldn't rule anything out, but we don't have any plans around [Warcraft IV] at this point. Getting [Warcraft III: Reforged] right, I think, is our priority first and foremost.
To be honest, I don't think that is too surprising. The focus of Warcraft will always be on the MMO, which is a continual revenue flow. The main story and major beats in the franchise are going to be told in there. Finding something meaningful to make out of a real-time strategy that would work with World of Warcraft seems… tricky. Although, perhaps one day that problem will be solved.