Really great and detailed, though one error I found. The Old Gods wouldn't want to help prevent the upcoming Legion attack but rather try to pressure it to happen. With the arrival of the Legion, it might cause enough damage to set free the Old Gods, and with the Old gods being unleashed and released from their prisons they would have the capability of taking over the whole Legion and defeating Sargeras. That was their initial plan during the War of the Ancients.While I know Wrathion etc have hinted at what appears to be the Burning Legion's return, I have a theory about a possible fifth expansion to set the stage first, so to speak. After the stuff going down between the horde and alliance in Pandaria, there is no way we would recuperate following Garrosh's defeat in time to face off against the Legion so soon. Instead, here is my guess at what's coming (I am willing to put money on this or something close to it being in expansion 5):
"World of Warcraft: Call of the Abyss"
Following the defeat of Garrosh and his Kor'kron horde, talk of peace has finally resumed between the Alliance and the Horde. Wrathion's grave warnings regarding Azeroth's future have begun to spread, and many of the world's denizens begin to feel a darkness approaching. Deep below the surface of Azeroth's swirling Maelstrom, something stirs...
Queen Azshara has made her presence known after millenia spent beneath the seas. Nazjatar, the sunken city and home of the Naga, has risen from the depths, sending forth the horrors of the Abyss into an already-fragile world. Seeking not to destroy Azeroth, but to unite it beneath her scaly fist, Azshara (and her Old God master(s)) believe they are the only hope of defending their planet against the coming of the Legion.
Following Azshara's defeat at the hands of Azeroth's guardians and the ancients of the Emerald Dream in the War of the Ancients 10,000 years ago, she was left to brood, plan, and prepare beneath the waters. Given her experience with the druids and their ancients, she and her Old God's minions preemptively sabotaged the Dream with their Emerald Nightmare, hoping to claim its power for their own. Much of Nazjatar is phased between the Dream and terrestrial Azeroth as a result.
Neptulon, lord of the Abyssal Maw, has once again called to the mortals of Azeroth for aid against Azshara's forces, who seek dominion over his realm in their unending conquest.
Malfurion and Tyrande, along with their Ancients, have again allied themselves with the Alliance and Horde in this new fight, but an old foe has been reborn from the raging energies of the Dream: Illidan Stormrage.
Seeking not power nor control, Illidan has come to our aid, having himself witnessed the War of the Ancients firsthand, now wishing to finally make his amends with the world, and repent for his crimes. Maiev, one his greatest rivals, seeks to reveal what she believes to be his greatest treachery yet, and destroy him once and for all. Malfurion, Tyrande, Maiev, and countless others find themselves torn between distrust and necessity in Illidan's return. This could even reignite a saucy love triangle between Malfurion, Tyrande, and Illidan.
Wrathion, interested in seeing if Azeroth's defenders can finally put aside their hatred and distrust, has begun observing from the shadows and aiding the most brave adventurers once more, for if we cannot learn to stand together now, there will be no hope in standing against the inevitable shadow of the Legion.
• New landmass of Nazjatar (8 or so zones), risen from the sea surrounding and containing the Maelstrom (maps from Cata can be changed to reflect this). Parts are still submerged, others merged with Azshara's horrific vision of the Emerald Dream, but all are dripping with the terrors of the newly awakened Abyss
• Increased level cap to 100
• No new classes (Pandaria gave us one, that's enough for now), but possibly a new neutral race (A splinter faction of naga, mayhaps)
• A new hub city a la Shattrath and Dalaran, as the Alliance and Horde practice their teamwork (Perhaps a pvp zone could be tied to this hub, since scuffles would be likely given the history between our two factions)
• More than one tier of raid content at release. Even if their availability is staggered, it still creates a feeling of more content (this philosophy also works for ten levels instead of five. Even if the time to level is equal to cata/mists launch, having ten levels and more zones feels more satisfying, imo)
• No all-underwater zones, but maybe more submerged areas within zones. This, and a submerged area in the hub city will allow for players to attain, and actually use, more aquatic mounts
• The Tomb of Sargeras (conveniently located in the sea) will be important, and involve something to toact as a segue into expansion 6. Maybe Azshara wants something of value there, but in doing so unwittingly allows the Legion to access Azeroth (since they always seem to have issues doing that on their own)
Small Expansion 6 Blurb:
Azshara's defeat will (ideally) secure Azeroth against the coming invasion, where we will be free to take the fight to the Legion preemptively via a revamped Outland, or at least new lands beyond Outland's portals, in expansion 6. Illidan's return will also allow for the training of a new league of Demon Hunters to aid in this first strike, so we can get that new class everyone seems to want (just not in expansion 5).
Edits: Fixed some grammar, typing on a tablet blows...