I believe it may actually be a new brand, possibly. Considering Hearthstone was one small project it could be a new team of a smaller size making this. It is certainly a multiplatform product considering the description, so perhaps a new f2p game?
It could also be WoW related or StarCraft 2+Diablo 3+WoW related in some form. Perhaps it has something to do with an older brand even? Lost Vikings? Will be interesting to see what's going to happen at BlizzCon.