The Horde and The Alliance dismantled. The final ending to the factions conflict.
All players from all factions can interact, group other and otherwise play with each other, including joining their guilds.
The war of the factions is over, the true war begins.
The shadowlands expansion proven true, the battle for azeroth begins (all the champions of the world rally together against the armies of the old gods).
Sylvanas has made a deal with Helya to save the spirits of all those who have been slain in the war, Teldrassil burned to save the night elves rather than destroy them, as Teldrassil was corrupted by the olds gods (no one knew this though).
PvP is conducted outside of the LORE, BGs, Arenas and such still remain relevant. Open World pvp is no longer possible.
This gives way to increasingly smart mob AI and increasingly difficult and highly dangerous zones. Dismantled factions also would mean one story for everyone, which means the story can be much better. (The current story is impossible to be a 50-50 between the alliance and horde, favoritism is not the exception but the rule.)
The last war will be likes of which has never been seen before, which both eclipses and dwarfs the decade old factions war as if they were mere toddlers playing. The entire universe is at risk of being completely destroyed by the Void Lords.
The Grand Finale of World of Warcraft would be the world’s greatest champions with the titans together going to the void to fight the void lords (at this point, to show the story in it’s true horror the game would be PEGI 18).
I would AT LEAST want to see the factions dismantled. The war is over, no one has won. The Horde lost the war. And so did the alliance. This is conflict for the sake of conflict. We protect nothing, we save no one, we fight and kill for the sake of fighting and killing one another.