A Legion themed expansion may or may not be coming. That said, regarding new races, there are some races iconic to both sides that each wants for different reasons but that still haven't made their way to become playable.
For Alliance the culprit is high elves, and for the Horde it's ogres. Players from both sides have expressed their desire to see these races added time and time again, even if some don't want to.
- for high elves the most clear problem is that they would essentially be the same to blood elves, only with blue eyes. So the Alliance would get a refurbished race... same lore, same looks as a Horde one, and if a new race is given to Horde, it wouldn't be nice as Horde get something new and shiny and alliance get blue eyed blood elves. If no race wouldn't be given to Horde, it would not be nice again as one race of the Horde would be made neutral tehnically.
-for ogres the most clear problems are size and general ugliness.
Yet both races have their adepts, going into lore aspects and general feel of the races and where they fit. So how could both races be fitted into their factions while bypassing the problems?
I present to you the idea of ethereal elves and crystal ogres as a possible solution(no pics, sorry, you'll need to use your imagination).
Alleria and Turalyon ventured into a portal as Draenor was ending alongside a small army of high elves as at the time the high elves were stationed a bit further away from the Dark Portal itself, in today's Netherstorm. And there they met the ethereals. And the ethereals saved them, but at a price! In truth they had only saved them to use for their experiments since the ethereals they met were a bunch of scientists who didn't care about morality and whatnot, they wanted to send their own energy into the high elven bodies to become flesh and bones again. So they used Alleria, Turalyon and the high elves as test subjects and found that Turalyon wasn't so good, as humans don't absorb magic so well, but high elves do!
So then, he continued his experiments on them, in an attempt to remake his race into flesh beings, since that's what the experiments of the ethereals there was about. But the experiments weren't going so well, the high elves were in horrible pain and they were starting to unravel too. So the ethereals started putting those bandages on them too. In the meantime Turalyon wasn't considered a threat as he was aging more and more, but that was their mistake, because at one point Turalyon broke free and blew up the machine used by the etherals, freeing all the former high elves, now ethereal elves!
They left the etheral dimension and reached a floating island in Outland. From there they made contact with the Alliance and rejoined the Alliance. Since being ethereal meant the high elves were not subjected to the hunger for arcane anymore, they shared it with their Azerothian high elf bretheren (only high elves, not blood elves) and turned them too into ethereal elves, thus sending the idea of high elves into oblivion. Alleria however did not want to share the idea with blood elves too, as she felt the blood elves betrayed the ideals of Quel'Danas! They had allied themselves with the trolls and orcs, they sucked fel magic and killed living beings and furthermore they banished some of their own for not agreeing with them!
The ogres of Ogri'la had been growing smarter on the mountains overlooking the other clans. They stood and pondered on how stupid the other clans under them were. If only they could share some of the wisdom the crystals had given them... but then the elders thought of a way! By taking some of the biggest crystals and blowing them up, they could spread some parts of the little crystals to their dumber versions down below. So that's what they did, they took some of the biggest crystals and assambled the ogre clans below. The ogres down there didn't understand what all those fancy words meant, but they stood for the free drinks and food. The Ogri'la ogres then blew up the crystals and splinters rained on all ogres but it didn't have the effect they wanted for the crystals shards reacted differently then they thought, they hit ogres like splinters and panic ensued. Some ogres were trampled by their own, some killed by the splinters.
The surviving ogres had splinters in their body, they could barely move yet they were lucky as the Horde fortress was close and the Horde saw all that had transpired and decided to take care of them. These few thousands of ogres were all in pain, yet they were the lucky ones, for many hundreads had died. The ogres showed little improvement, and in plus the crystal formations seemed to grow and the ogres to shrink. At long last, after months, one of the ogres awakened. His body was partially covered in crystals and he was smaller and different in a way. He then spoke, yet it was not the broken language ogres used to speak, it was clear and sounded smart. He had been made smarter. Soon others awakened, all smarter and smaller, and they decided to put petty hatreds aside and unite. As thanks for the help the Horde had given them in taking care of them, they'd join them in the Horde.
From a distance etheral elves look similar to high elves, yet when you get close you can see the difference. You can see their ears popping out and their blue eyes, but parts of their body are bandaged with those ethereal bandages, and the skin under seems to flicker in and out of existance, sort of like ghosts. You can imagine, half bandages, half high elf, and the space between pure energy. And the bandages seem to be part of them, I mean, like come out of their skin, on the face this would be seen best, the center of the face seems regular elf, though a bit transparent, but on the sides the skin starts to unravel into those bandages forming hair and going down on the neck even.
Think of it this way, in the center you have their face, a bit ghostly. from the ears, the neck and hair, it seems to unravel radiating bandages towards the back of the head, like an octopus. On the body, the bandages seem to unravel around the hands (their hands seem to be made fully of bandages, like you've cut them out of paper and put them on the elves), same on legs, and also around their chest, leaving a trace of energy in the middle pulsating outwards.
The ethereal elves have the typical ethereal movement, like they're teleporting over.
Crystal ogres look quite different then their counterparts. They're smaller, the size of tauren, they are also a bit slimmer from the time they were in a coma and didn't eat anything.
Besides these changes, parts of their body are covered in strange crystals, making it look like those parts of the ogres are actually made out of crystal. In general much of the parts between joints seem to suffer this problem, leaving it seem like pieces of meet grow into crystals there.
Being slimmer, they look more similar to pandaren in body type, just a tiny bit chubbier, yet also taller.
Ethereal elves - warrior, rogue, paladin, priest, druid (the high elves knew some things about druidism, not much, but combined with the etheral knowledge and machines, they managed to control nature by force rather then by asking it, kind of like the difference between tauren and taunka regarding elements), hunter, mage, death knight (some high elves that had been raised were not accepted by their blood elven bretheren because of the prejudice against high elves, and were left without a home, wondering the world, they were taken in by the Alliance out of pity more and now the ethereal elves felt simpaty for their plight since it's similar to theirs and transformed them into ethereal death knights as well, with the mention that in the death knight starting area you're a regular elf, and at the end you get turned in a etheral elf before you get sent to SW, more out of in-game mechanics then actually what happened) and warlocks (yes, the ethereal elves are a bit hypocritical, accusing the blood elves of using fel yet still using it themselves, I think it gives more growth potential into their lore) . So ethereal elves can't be: shamans and monks.
Crystal ogres - warrior, rogue (their smaller stature permits them to go unseen, and they can use the crystals in their body so sort of alter perception, making them able to be rogues), priest, shaman, hunter, mage, warlock, death knight (ogres did die as ogres were on Azeroth at the time when the Lich King started his attack so not unbelievable) and monks (some went and learned the monk style of balance as they wanted to learn more. So they can't be paladins and druids.
Ethereal elves ride ghostly unicorns (what can you do, all their actual unicorns died, they brought some back with the ethereal knowledge, but they're not perfect).
Crystal ogres ride giant fel boars.
Mention, as I didn't have time to draw something, you'll have to use your imagination of what I explained.
So what do you think?