If there are going to be 2 more hero packs, and the next is indeed druid then the third should be something completely different. 2 revisited classes is enough nostalgia/fan service. If they were given creative freedom lets see what they can truly come up with that gives us a real fresh experience.
Does playable class have to be a human? How about a Khazra hero! Or a demon who defects? Happened with Lilith right? If the nephalem angle has to be retained, and they have to be human, how about one of those cultists? Theres already a bounty where one comes good.