Warlords of Draenor is the first expansion to have neither a new playable class nor a new playable race. In fairness, Blizzard earned this little reprieve after Mists of Pandaria gave us one of each (the unfortunate result being that about 95% of Monks are Pandaren, and vice versa, though even now I'm starting to see that trend smoothing out, much as Draenei Shaman and Blood Elf Paladins did over time.) We also can't complain too much because all the vanilla and BC races are getting total revamps with new character models (sadly, Blood Elves are going to have to wait until a later patch - though I'm confident it will be on or before 6.1.)
But we know that WoW is planned for another two expansions, and they're going to keep making them for as long as people are willing to play them (if Everquest can still be online, you can be damn sure that WoW is going to be here for years to come.)
And races are a lot easier to implement than classes. Classes will fundamentally shift the game's balance, requiring more specs to be balanced against other specs and the need to create new abilities and talents with each expansion. Creating a new race does require a lot of work from the creative team, and they need new models, and a new starting zone, new mounts, and depending on their class choices, they might need their own totem, animal form, or Paladin mount.
But races are largely a kind of "fire and forget" addition to the game. Once they're in, they're in, and other than the occasional tweak to racial abilities, they will remain balanced. And from there, they just give you additional options for building new zones and quests (some options I wish Blizzard would use more, like Worgen. Though I'm happy to see the Draenei getting an expansion in the spotlight.)
So I think that over the course of the game, we'll see more expansions that give us new races than classes. There are some who think we already have more classes than we need, to which I say HEATHEN! But it's clear that, mechanically, the game could have twice as many races and still function the same way. The trend has borne out pretty well, with three expansions giving us new races and two giving us new classes. I certainly hope that there will be a new class in whatever expansion follows Warlords (Demon Hunters, c'mon, you know you want them,) but I do think races are a more likely eventuality.
However, restricting both of these additions is the problem of lore. Generally, it's best for these things not to come out of the total blue. Every new race and class had at least some precedent in-game before they were introduced. Blood Elves were well-established in Warcraft II and III (though they were High Elves for most of that time.) The Draenei did, in fact, show up in Warcraft III's Frozen Throne expansion, though we only interacted with Akama and his Broken (who used Lost One models in TFT.) The Draenei did require a retcon, which changed it so that the Eredar demons were not originally demonic, but had been corrupted. Still, despite that hiccup (that Chris Metzen apparently still feels embarrassed about,) the Draenei fit pretty nicely into the world, and also fleshed out the early history of the Horde.
The Goblins had been a presence in Warcraft since WCII (easy guide here: if it isn't a human or an orc, it was introduced no earlier than WCII.) Perhaps the only lore acrobatics required for the goblins was to establish them as Horde-only, as the goblins found in WoW up to that point were decidedly neutral. Still, simply by establishing the Bilgewater Cartel as separate from the Steamwheedle Cartel, it was pretty easy to make them fit.
The Worgen were introduced in Vanilla WoW, with presences in Silverpine Forest, Duskwood, and Ashenvale. Given the locked-off nature of Gilneas and the huge prevalence of Worgen in Silverpine (it was by far the zone they had the greatest presence in,) it was always strongly suspected that the humans of Gilneas had been turned into Worgen. Cataclysm basically just confirmed this rumor, but it also confirmed what had been hinted at in Vanilla, which was that the Worgen curse was related to the Night Elves and Druidism.
The Pandaren probably caused the biggest uproar, as they had, for a long time, been considered by many to be a non-canon joke - the product of an April Fool's joke on Blizzard's part. Still, while that may have been their origin, Chen Stormstout was a real presence in the Frozen Throne's "Founding of Durotar" campaign, and hints of his presence remained, such as the quest "Chen's Empty Keg" in the Barrens.
So what does this all mean for future race choices? Well, it seems to mean that one cannot simply pull a playable race from thin air - there must be some background in-game to allow them. What this does imply, though, is that whatever new races we get, we've probably already heard of them.
So who are the prime candidates?
Ogres:
Ogres have been around since WCII, and have traditionally been allies of the Horde. The Ogres are from Draenor, like the Orcs. Right now, there are only a few obstacles to making them playable. First, we've never seen a female ogre. But that didn't stop us with the Worgen, so cross that off the list. Second, they're absurdly large. Do we really want a race bigger than the Tauren? I could see them maybe revising their size downward, but that might feel like a cheat. Third, most Ogres are dumb as a sack of bricks, and the smart ones need to have multiple heads. Granted, maybe you could have fun with that. Or you could make the faction of playable Ogres a more enlightened one (albeit not too much, or you'd lose the personality of the Ogres.) The two-head thing could actually be interesting - perhaps Mages and Warlocks would get two heads while other classes would get only one. And helmets could be duplicated the same way that you give everyone two matching gloves.
Naga:
Another long-runner, the Naga have been round since The Frozen Throne. They have a rich history, but even more than the ogres, they have anatomical issues. As serpent-people, they don't really have legs. While gear I think could be handled by making pants into a kind of tail-cover and boots into a kind of cap on the end, it also does lead to some problems with, say, mounts. It's not insurmountable, though, and I'd like to see what they come up with to solve those problems, because the Naga are pretty cool. The Naga do have one big advantage, which is that there are already models for both male and female Naga, though one wonders how one is to deal with the whole "female Naga have lots of arms" thing.
Ethereals:
The Ethereals were actually not even that big of a presence in Burning Crusade, which was their debut. But there something about them that's wildly appealing. They are ruthless capitalists, but they are not crass like goblins. Again, there are anatomical obstacles here, but I think as long as one treats the bandages that hold their form together like skin (with patterns in their face-bandages being used to portray eyes and mouths and such,) you could have a very cool-looking race.
Arrakoa:
If you had suggested Arrakoa to me before I played the Warlords of Draenor Beta, I would have said "meh, they're kind of boring." But now there's a really cool backstory to their society. I suppose the question would be whether to give us playable healthy Arrakoa, or the twisted, cursed ones (which were the only ones we saw in BC.)
Vrykul:
The Vrykul were a big presence in Northrend, and their connection to humanity is pretty intriguing. We only interacted with a handful of friendly Vrykul, but with King Ymiron gone, one wonders if the Vrykul might chill out enough to consider joining up with the little guys who came to Northrend in 2008. Again, though, like the Ogres, there is the issue of size here. The Vrykul are half-giants, and much larger than humans kind of by definition. Still, unlike most of the races we come across, there are both male and female models for the Vrykul, so... that's a starting point.
Tol'vir:
Haha, just kidding. Who gives a crap about the Tol'vir? Maybe the least personality of any introduced race.
Just About Any of the Many Pandarian Races:
One of the things I loved about Pandaria was the wide variety of interesting people beyond the Pandaren. The Jinyu, Hozen, Grummles, Mogu, Mantid, Yaungol - they all had their own distinct personalities. Right now, we're all a bit burnt out on Pandaria (and Orcs, but tough luck about that!) and it's a good possibility that we won't really be revisiting that setting ever again. Still, if you could work it out, there's a lot of potential in there for playable races. Hell, the Jinyu and Hozen already kinda sorta joined the Alliance and Horde, respectively.
There are a lot of other races out there that, with a bit of tweaking, could make for interesting additions to the playable options. It'll be a long time before we hear anything about the next expansion (probably not until Blizzcon 2015) but it'll be interesting to see what kind of characters we'll see pop up next.
