I honestly wouldn't mind a troll hero, either. I was hoping they would make Vol'jin the alternate priest but then they made him a card.
Maybe they could make Zul'jin the alternate Rogue? But then Garona wouldn't be the alternate Rogue, and that makes me sad. =(
I think Zul'jin is a decent option. Blizz has shown a real reluctance to go with the more "non-standard" races. I mean, look at all the races that haven't been represented yet - Tauren, Troll, Goblin, Gnome, Worgen, Dranaei, Forsaken, and Pandaren.
Of those, I feel like Dranaei, Troll, and Forsaken might be close. Maybe even Worgen. I don't think you'll see Garona, because we already have a female, Horde-based rogue. They'll probably want to make a male skin for all of the players out there who have problems playing as a female. I think your choice is pretty cool. I think a Worgen would be cool as well. I feel like Blizz will go with a human though - maybe someone from SI:7.
I think male Tauren, or possibly female Troll is what we're going to get for Druid. Male Tauren kind of competes with Malfurion though, so probably not. I can't see players going for a female Tauren though.
I think a Forsaken priest would be awesome, but if I'm completely honest with myself, I just want Tyrande. Having her as a hero means that I can just buy her instead of having to craft her. lol
I think Warlock will get a male Worgen or a female Human.
I think Pally will get a Horde female, but I can't seeing it being Tauren because no one (but myself) would play with it. Female blood elf pally is possible, but kind of clashes with Valeera.
I'm pretty excited about Shaman. Shaman's gotta be a Draenaei, and hopefully female. We already have Horde-based totems. I think Draenaei gives us the possibility of new totems, plus female Draenaei are hawt. I hope they don't go dwarven, and I really hope they don't get lazy and just do another Horde shaman so they can reuse the existing totems.
tl;dr - Start mixing it up, Blizzard! Worgen, Forsaken, Trolls, Draenei, and Tauren are cool too! (But don't forget Tyrande!)