Time to lay out some predictions.
Bear in mind that anything can happen when Blizzard puts their mind to it, and I think they're building up to something very interesting in the shakeup within the horde (especially given the new lines we get for Lor'thremar in 5.1). Please see these for what they are (a huge wishlist)
Blood elves become Neutral: For game purposes, this is done to show what happened because of the civil war. Lore - Though Lor'thremar had his moment of doubt, he has reaffirmed his place in the horde now that Garosh is out of the picture. Unfortunately, many blood elves don't agree with his decision and have rallied behind Vereesa Windrunner. With Rhonin's widow to vouch for them, they rejoin the alliance and once again call themselves high elves. Existing blood elves remain loyal to the horde. New blood elves get a starting quest line that ends in them choosing a faction.
Return to Outland: With the Legion's cover blown, both the horde and the alliance are scrambling to learn what they can do before the impending attack. To this end, the horde reaches out to Rexxar and the Mok'Nathal to learn more about what happened in hopes of preventing it. To prove her loyalty to the Alliance, Vereesa travels to outland to meet with her recently returned older sister for similar reasons. After being away for so long from her family, Alleria decides to remain neutral to the factions after meeting with both Vereesa and Sylvanas. Sylvanas keeps herself at arms' length, though, so her story with the others isn't as strong.
Outland 90-95: The new continent is a transformed and somewhat rejuvinated Outland. With the Maghar finding faith in Shattrath and learning druidism from Azeroth, they have been hard at work making what's left of their world liveable. Like a cancer that has to be cut out, the goblins and the Ethereal have
severed Netherstorm from the rest of the region so its continued unravelling wouldn't affect the rest of Outland.
Hellfire Peninsula (94-95) is the official PVP zone now and there are alliance/horde strongholds where once were but camps. Players will be offered safety by their factions upon entering through the dark portal, but woe unto those who fly out beyond their influence. The real questing begins at
Shattrath and Terokar (90-91), and players can safely purchase a taxi there if they want. With Netherstorm gone, the
ruins of Tempest Keep and Kael'thas' remaining loyalists have used the last of their power to
fly to Nagrand (91-92/95), where they have now crashed and are frantically trying to reactivate the portal there for some sinister purpose.
Shadowmoon valley (95-95) is now a training ground for Demonhunters as they battle the remaining legion strongholds built there.
The Bone Wastes are gone(90-91), and
Auchindown is restored thanks to the Sha'tar.
The ogres of Blades' Edge (93-94): have cleared out the legion, the netherwing, and the black dragons and are setting up their half of the area to welcome the horde while the night elves continue to hold back the arrokoa and look for aid from the alliance. Finally,
Zangarmarsh (92-93): is now a lush forest again, where the goblins are actually using their teraforming for reasonable purposes to expand the land while the druids grow new life on what has been created so far. This is done in part with the remnants of Netherstorm, and the goblins have even relocated Area 52 here. In honor of their new home, they call it Area 56.0. It'll be renamed with each patch through the expansion...
Ogres Join the horde: Now that Rexxar is around, the ogres of Azeroth and Outland finally declare their membership within the now scattered horde. They use Worgs as racial mounts, similar to orcs. To make up for the "similar" mount issues, Tauren finally gain plainsrunning back as a racial ability to match the Worgen's Running Wild.
The Dragonflights:After the loss of their power, the dragon aspects have started trying to cope with their new mortality as well as their weakened powers.
Kalecgos: is busy with Jaina.
Nozdormu broods over his part in the hour of twilight and starts sending bronze dragons out across Azeroth and Outland to help adventurers see the past and learn from their mistakes.
Yserahelps new druids in azeroth (maghar and draenei) learn to navigate the Emerald Dream.
Alexstrasza has come to outland with Nozdormu and has adopted the nether drakes into her broken family. Meanwhile
Wrathion, travels to outland to face his brother and investigate his father's former home while avoiding notice by the aspects.
Time Jumping:To facilitate a new outland continent (90-95), the Bronze dragonflight are available throughout outland to speak to and jump between 60-70 content and the current. Similarly, they can now be found in several other parts of Azeroth, offering pocket instances where players can enjoy past events/dungeons/raids. Simply speak with a bronze dragon at any of the known locations to que or get a blast from the past
(60 onyxia returns, as does Zul'aman/Zul'gurub raid, and naxx 40 exactly as they were). This also paves the way for other updates in the future and shows why Nozdormu still eventually becomes Murozond. Of course, we get new reason to raise faction with the brood of Nozdormu, because having exalted with them means you get an on use item to jump yourself when out of combat (with some trivial 15-30 min cooldown of course).
Demon hunter class: With the bronze dragonflight now more lax in their methodology, repercussions can already be seen starting to form in outland.
After Akama used the Soulcore at the Black temple, the half-demon nightelf, Illidan, was either returned to life or called from the past (we find out which in game) just before he was killed by Maiev. When word of the coming invasion of Azeroth reaches him, Illidan begins recruiting
(night/blood/high) elves, humans, orcs, and trolls in order to train the strongest among those races as Demon Hunters.
Class Restrictions Loosened: In order to survive what comes next, the fractured horde races must do what they can. To this end, Baine BloodHoof turns to a rebel group of Grim totem (no longer under the leadership of Magatha) and brings them under his people's wing.
Tauren gain warlocks. In their attempts to restore the land that was damaged when first they arrived, the draenei have turned to the nightelves for help. Now, some members of the race follow a new path.
Draenei gain druids.
Sub Races to explain classes: The races of Azeroth and Draenor must unite more than ever before if they are to stem the tide of war against the Legion.
Maghar, Taunka, Broken, and vrykul are now available as playable options for orcs, tauren, draenei, and humans respectively. In some cases, these subraces come with new class options, including
Vrykul Shaman, Broken rogue/warlock, Maghar priest/druid and Taunka mage.