[Spoilers] As Legion ends, here's where it looks like the story is going next, to me.

We have plenty of hints and there's already been a ton of discussion on this so here's just putting them together in a basic plot that actually makes sense. TL;DR at bottom.(7.3) Legion ends with Sargeras defeated, his spirit imprisoned in space where Illidan and Maiev will guard him indefinitely.Here's the pitch in italics (elements explained and/or listed after):With Sargeras imprisoned, no single entity is powerful enough and disposed to destroying an entire planet. That threat eliminated, the agents of the Void seize the opportunity to manifest in Reality against the agents and force of the Light, on Azeroth. N’Zoth facilitates destruction upon the defenders of Azeroth not only directly but with the Naga. Queen Azshara has ever been led by the glamour of powerful beings promising grandeur for cooperation–first Sargeras, then the darkness which gave her and her followers what she could not as they sunk into the abyss. Now land from the ocean floor is pushed to the surface, sprawling out from the edge of the Maelstrom, bringing armies and cities onto the planet’s surface. Kul Tiras, which had been pushed westward away from the Eastern Kingdoms in the Cataclysm, and Zandalar, which had been drifting towards the Maelstrom since the Cataclysm, are now just off the coast of (if not on top of) this new landmass.The Void, from which the Void Lords came and Void energy is pulled, is the cosmic force which the Old Gods and others are aligned and natured by. The power of the Void and Void energy has an immense draw consciously, physically, and subconsciously. The dead in Nagrand and Shadowmoon had their spirits drawn towards the darkened Naaru in Oshugun and the Dark Star, just as that on Argus draws the spirits of the dead forth and keeps them from resting or leaving.Void energy has also turned those who seek to harness it, into serving its vision: alternate Ner’zhul tapped into the power of the Dark Star and is defeated at the Edge of Reality, one place where Reality and the Void are closest. Main universe Ner’zhul was aided by the power of Yogg Saron and the Nerubian Empire he had once controlled, and broke his will free from the Legion to fight against the Legion, especially Kil’Jaeden, who had both personally tricked him into enslaving the Horde to the Legion and had destroyed his body and bound his spirit to the armor in the Frozen Throne. Having agreed to assist the Knights of the Ebon Blade in order to exercise vengeance upon the Legion, now not only is his personal nemesis, Kil’Jaeden, defeated, but Sargeras and the whole crusade itself.While we have known since Burning Crusade that the Etherium has been seeking to “become” Void, we see them return in Legion trying to do so in the Nexus (where we stopped them) and on Argus, where the Void energy of a dying Naaru has drawn Ethereals who we defeat in the 7.3 dungeon. As the Void and Void energy is the source and power of the Old Gods, there will likewise be a strong and obvious source on Azeroth to draw the Etherium.The Void - Cosmic Force opposed to The Light; manifests first in Void Lords who in turn created Old Gods to throw into space randomly and hit planets. - The Etherium is drawn to Void energy (Argus dungeon, Netherstorm, the Nexus).Old Gods - N'Zoth lies under the ocean. His pre-Sundering location looked to be south of Suramar, but he could have moved in the Cataclysm.The Cataclysm moved the ocean floor around and Azeroth's physics don't make sense. It pushed Vashjir up, pulled Kul Tiras away from Gilneas, and started moving Zandalar towards the Maelstrom. It also broke open a connection between the Maelstrom and Deepholm.(I imagine new land surfacing from around the Maelstrom looking like the map of Lex Luthor's Kryptonite continent in Superman Returns, but without the physics).Lots of whispers (Il’gynoth, the Puzzle Box of Yogg Saron, Xal’atath) relate:Il'gynoth• To find him, drown yourself in the circle of stars.• Her heart is a crater, and we have filled it.• At the hour of her third death, she will usher in our coming.• From the earth, he draws strength. Our earth. Our strength.• Its surface blazes bright, masking shadows below.Puzzle Box• At the bottom of the ocean even light must die.• The stars sweep chill currents that make men shiver in the dark.• The drowned god's heart is black ice.• It is standing right behind you. Do not move. Do not breathe.• In the sunken city, he lays dreaming.• The fish know all the secrets. They know the cold. They know the dark.Xal'atath• I long for the day our masters can truly pass into this realm. You have only seen fragments, shadows; the faintest of echoes. Ask the Ethereals what one of these manifestations are capable of. (at Star Augur Etraeus)• Xal'atath whispers: Xavius, running from one master to the next, scrambling for power, yet defeated again and again. The God of the Deep picks a poor champion? Or, is there something else at play? (when facing Xavius)• It took ages to make my return to the surface after the Sundering. The naga can be so possessive of artifacts.• I can feel the pulse of your world quickening. Soon, all will be drenched in its life blood. (after defeating Kil'jaeden in Tomb of Sargeras)Maelstrom• Some have pointed out that looking up from Deepholm, the bottom of the Maelstrom looks like it has stars.• The Maelstrom was the Well of Eternity pre-Sundering, which earlier had been a crater/wound in Azeroth where Y'Shaarj's body dug into the crust before it was yanked out by Amam'thul. Azeroth's blood is arcane, and the wound was stopped from bleeding by surrounding it with magical wards. The Well was also called "the true heart of the world's magic and natural power". We also see in the new Magni scenario that Azeroth's "heartbeat" somehow is monitored through the small wells inside the rooms.Azshara/Naga• In Azsuna, Athissa calls Queen Azshara "The Light beneath the Tides".• Whether Azshara wanted to keep us from getting the Tidestone, once the Tomb of Sargeras opened for the Legion, was to help the Legion and be rewarded by Sargeras, to prevent the hour of the Old Gods from coming, or for her own, unrelated use, it's unclear if she'll be completely in league with N'Zoth or not once he reveals himself and his plan to the world.• The Scepter of Tides, the Shaman Resto Artifact, was given to her by Xavius when she became Queen, magically made her beautiful and powerful, and kept her and her highborne servants alive during the Sundering as they were swept away into the abyss until they needed a darker power's help to survive.Important sources and suggested reading:World of Warcraft: Chronicle Volume 1Wowpedia (Not Wowhead):Xal'atathIl'gynothPuzzle Box of Yogg-SaronWell of EternityScepter of TidesVoidTL;DR Sargeras is no longer a threat, so N’Zoth pushes up a continent around or near the Maelstrom where the Naga and Azshara built their cities. Kul Tiras and some other islands are suddenly next to or a part of the new continent. The Etherium is drawn to Void energy sources (like Old Gods). The Lich King got his revenge on the Legion but made a pact with the Ebon Blade, and also has a past with Yogg-Saron, so he’s probably up to something.