Out of curiosity I did some googling and looked at blizzard's website, Icy Veins, and the heroes of the storm subreddit and I didn't see any news about the next upcoming hero. I'm keenly interested in it too as I feel as thought we should be seeing our next hero soon, but I could be wrong.
Blizzard's release schedule seems to be nothing if not sporadic so who knows? I do hope whomever they add is at least interesting! If they did add a new hero who would you want it to be?
Most rumors point to something happening on the 5th as they have the Second Anniversary live stream going on. Lots of people speculating, but not even a whisper of real information. The IP with the furthest removal from a release would be Warcraft, but that doesn't mean it will be a WC hero. Personally, I'd love a new support!
If I could have a wishlist it would be a hero from diablo 2. Cassia was cool but as a character she doesn't resonate with me very well. I want more Diablo villians! They were fun and always had interesting and unique abilities. Many of whom I personally have very fond memories of.
Heck, even more diablo 3 villains! I know it's 'heroes' of the storm but come on let's have some baddies!