Since leak season is upon us, I thought it'd be fun for us to goof around with ideas for the story of 10.0, keep in mind i'm not talking about gameplay features but the basic premise going forward from shadowlands
We return to Azeroth through the shadowlands breach at Icecrown, once we arrive the portal closes behind us however Icecrown Citadel no longer looks how we left it, monuments and tombs are built on the citadel to Azeroth's heroes, Jaina, Thrall, Anduin, etc.
We meet a disheveled, older Genn holding a vigil with the Ebon Blade who can't believe we have returned, 10 years have passed since we entered the Shadowlands, Genn informs us that the scourge threat was completely underestimated when we left, when we left millions of scourge began to pour out of Azjol-Nerub, sealed there by Bolvar over the years he took command of the helm of Domination, with the helms destruction the scourge slowly began to realize that the wards no longer held them and began to filter out in massives waves.
Genn informs us that spread of the scourge couldn't be contained, Stormwind, Ironforge, and Lordaeron have been completely overrun and most of the alliance and horde survivors built Silvermoon and the surrounding areas into a fortress, on Kalimdor, the entire continent was overrun, the only city still standing is Dalaran which has been moved above Mount Hyjal, Icecrown Citadel is all that remains in Northrend with the Ebon Blade numbers dwindling without a Lich King to create more.
Genn tells us that roughly a year ago something strange occurred that shifted the invasion, the scourge invasion went inert for a short time, what followed however is where we find ourselves today, some scourge have regained their former identities of who they were, skirmishes within the scourge broke out everywhere with some battles resulting in a withdrawal from attacking the living whereas some battles led to increased attacks, however in Northrend, the oldest of the scourge forces seem to have completely withdrawn back into underground networks of Azjol-Nerub.
What awaits us when we return to Azeroth is the world Arthas envisioned made manifest, however, this time the greatest heroes of Azeroth weren't there to stop it and without a Lich King to control the scourge, we will have to retake Azeroth one step at a time.
I was gonna add Pandaria to the mix but I don't think lore-wise the scourge could reach that far down, unless the nerubians have been super busy tunneling down to Panda land.