Medivh is now live. He's a ranged specialist with a lot of powerful group-support abilities (honestly, I think they could have labeled him support.)
But what's interesting here is that they've also basically told us who's coming to the Nexus next, and it's Gul'dan.
Other than Azmodan's "Azgul'dan" skin, we haven't seen Warcraft's worst mortal (Arthas gives him good competition, but he's already the Lich King in his Heroes of the Storm version and frankly, even at his worst, he might still lose out to Gul'dan.)
Given Gul'dan's prominence in both the recent Warcraft movie and the upcoming Legion expansion, I'm not surprised to see that Gul'dan's coming to Heroes of the Storm. I'm eager to find out what abilities he has, because we actually haven't really ever seen Gul'dan in combat except in cutscenes, and even only rarely then.