These are the most likely expansions to be featured in World of Warcraft. Chris Metzen has confirmed that Blizzard has already thought of about 5-6 more. Here's what we think.
Emerald Dream expansion
For a long time, people have speculated that there will be an expansion based on the emerald dream. Though the emerald nightmare has been very much reduced in size, it still exists.
Lore: The people of Azeroth have begun to encounter the emerald nightmare more often. As the problem grows larger, the people of Azeroth realize that they cannot defeat N'Zoth, the Drowned God (see Puzzle Box of Yogg-Saron), physically. They must kill him through the dream. For the first time, Elune becomes an NPC and guides you in the Emerald Dream Raid. Also some background: The city in Puzzle Box of Yogg-Saron reffers to the place where N'Zoth once dwelled. He corrupted the inhabitants, and, during the Shattering, the city was flooded. N'Zoth was forced to create the Nightmare for him and his people to survive in. Now you must stop him.
the Flaming War expansion
The final faceoff with the Burning Legion.
Lore: Though Sargeras is trapped in Azeroth, Illidan Stormrage is still alive, using the lastbits of the well of eternity. He makes a pact with the burning legion to invade Azeroth. Illidan opens a portal in the second Well of Eternity, letting the burning legion invade Azeroth. The legion frees Sargeras. Now Azeroth must call on the help of those who were once their enemy but also do not wish Azeroth to be taken over: the old gods. The old gods are freed and help fight the burning legion. Finally, Illidan is killed and Sargeras once again trapped. The old gods make an agreement with Azeroth: If the people of Azeroth provide food for the old gods, the old gods will help defend Azeroth.
Lore: The Gnolls, Troggs, Murlocs, Harpies, Satyrs, and Kobolds of Azeroth have been brought together by Ragnaros to make a pact to work together as "the Ragnarok Clan" and bring an end to the alliance and horde. Great wars ensue as Azeroth as we know it changes, and we face what could be one of the greatest wars Azeroth has ever fought. This could all lead to having "rebel" Gnolls, Troggs, Murlocs, Harpies, Satyrs, and Kobolds who can now be played and are neutral until lvl 10.
the Other Side of Azeroth
We all know if we look at the planet of Azeroth that there is another side to it. We also all know that people who have set sail for it have never returned.
Lore: Though this could be an expansion, I think it would be better as (a) a patch or (b) simply released along with battle of Azeroth. Anyway, the lore is that Azeroth can barely hold off the growing armies of the Ragnarok Clan, so they decided to get help from the other side of Azeroth. This could definetely bring some new races.
Expansion, patch, or released with Ragnarok?
Seperate expansion: Because it would be nice to be able to play the races in Ragnarok expansion, AND it would be nice to have some new playable races in the Other Side of Azeroth expansion. But altogether in one expansion would be a lot, so it should be seperate.
Patch: Since it follows with the storyline of Ragnarok , it could be a patch. Only problem here is that new races have never gone into play with a patch.
Along with Ragnarok: Since this is pretty much part of the Ragnarok lore, it could be the same expansion. But releasing that many races in one expansion is a lot...
Since technically Azshara is still alive, this would be cool.
Lore: Azshara was nearly killed by Vol'jin and survived. She waited for a long time and now, finally, Azeroth has been very weakened. With the Other Side of Azeroth it is revealed that Azshara has been dwelling there for a long time. Now that she has been discovered, she has no choice but to strike now with her forces of Naga.
Bonus: New Class and Race ideas
Necromancer, Acolyte, Demon hunter (Hero Classes), Brute, Sorcerer.