Which would they be? It could be previously existing races, like Furbolg or the Ankoan, or something new and creative!
Personally, I would add Dryad/Keeper of the Grove (maybe Dryads are female and Keepers are male? idk), Tuskarr, and Harpy (I don’t care they can only be female).
Honorable mentions to the Centaur and Kobold.
WoW has so many unique races that we never even get to play. What ones do you guys love?
Just swinging by to add my vote for high elves!
I’m greedy for more horde monster races and a sucker for beastly-looking ones, so my go-tos would be drakonid, naga, and either saberon or gnolls. Probably gnolls; since they could play up a comedy role the other two largely don’t bring.
Edit: Back before Cata came out, I thought worgen would’ve been perfect as a forsaken-relatable race that could play up a sympathetic werewolf angle with humans as their enemies, but RIP to that.
Sethrak since they would have been better than vulpera
Ogres cuz they’ve been part of the horde forever
Naga since we’ve seen groups that aren’t loyal to aszhara anymore
The 3 playable races I would like to add:
I would like to add these ones too:
)The 3 playable races I would like to add as customization:
The 3 playable races I would like to add but I’m pretty sure it won’t happen:
Mogu, Broken / Krokul, Forest Troll, Hananir, Vrykul and Saberon are the races I’m waiting the most as playable race. 
Cat people.
That’s all three of my votes.
Edit: Ok, FINE
Jinyu/Hozen
Saberon/Arrakoa (These could both probably be for both sides, maybe)
Ogres/Tuskarr (Give the Ogres to the Horde and to make it even give Tuskarr to Alliance).
I believe you’re talking about new races, not allied races. 
Succubus, Shivarra and Harpy.
Allied Races are just fancy fantasy speech for “Unlockable Races”. A lot of people seem to think that reusing a regular race is necessary to consider it an Allied Race, but the Kul Tirans have a completely original model.
Not only that, you also have the Dracthyr, a base Race that reuses Human and Blood Elf models.
Base Race = You get it by default; Allied Race = You have to unlock it. That’s the whole difference.
No, I mean that they would be Allied. I think it would be cool if there were quests you had to do, to learn more about the culture. And besides, a lot of these races are not very trusting. You would have to gain the Harpy’s trust, for example, meaning you have to level reputation. This makes them Allied races. 
Ogres on horde like we should of been had!
lelves, they are like void elves, but more lightforged
selves, subterranean elves using void elf models, basically like void elves, but with less void
felves, like void elves, but with fel instead of void.
Happy 4/20 and Easter, lmao.
I would sacrifice all three allied races in a wickerman just to get the same level of customization that Orcs got across all the current races.
But if that’s not an option:
Gnolls
Naga
Nerubians
Worgen also have a similar ability using human visages. 
It’s possible although we should get a new design for the model and new locations. Remembering how goblins were added. 
I don’t think I would add new races. We seem to have enough to choose from. What I would do is add a fourth spec to every class and then go through and thoroughly balance each. I wouldn’t listen to the people yelling and screaming about homogenization, but I would focus on balance.
ooooh Sethrak and Naga! I feel like Sethrak have such a rich culture, they are just so perfect. I absolutely adore them and even though I love Vulpera it’s a crime we didn’t get both.
Saberon - Horde
Arrakoa - Both with the option to use both models.
Sethrak - Alliance
Honorable mention:
Broken - I could make a case for them being available to the Alliance and Horde.
would have to be neutral the horde and alliance help them out in wrath
Eh points to Nightborne
It does not always work that way. I always felt they would be more Horde or neutral because they did not want their mutant weak children (humans). So I can see some of them wanting to side with the physically stronger Horde races that also have a similar value system. I can also see some of them feeling a protective urge for their weak children and going Alliance for that. It would be more of a MoP Allied race story than TWW Allied race story.
High elves won’t be able to function correctly because of their addiction.
My 3 are:
Murlocs
Naga
Vrykul
All 3 can be both factions.