
Vol'jin is going to be confronting the Lich King. Bwonsamdi is also involved in this scenario. Why Vol'jin is doing this is unknown but it is speculated that Bwonsamdi's "boss" is the Lich King.
Tyrande returns to Darkshore and undergoes the Ritual of the Night Warrior. Night Warrior is one of the titles of Elune, and it looks like Tyrande is possibly becoming an avatar of Elune. Upon completing this questline, other Kaldorei will be able to customize themselves with the aesthetics of the Night Warrior.
The Blood Elf Heritage Armor questline involves returning to Quel'thalas and reliving the events that led to the destruction of the Sunwell.
The Dwarf Heritage Armor questline involves returning to Ulduar, though exact details are unknown at this time.
For some reason, the Horde free Ashvane and other prisoners from Tol Dagor.
In the Darkshore Warfront, efforts are being made on both sides to rebuild Auberdine and Bashal'Aran as settlments/forts.
Xal'atah is still around, though dormant. A Quest Item-version of her has been datamined.
Sylvanas is sending assassins to kill Saurfang. You get a hood and cloak to disguise yourself in order to try and throw them off of his trail. The hood and cloak have the flavor text "Some revolutions begin with the smallest acts of defiance." So it looks like Blizz is potentially paving the way for Saurfang to overthrow Sylvanas.
Sylvanas is also raising Kaldorei as Dark Rangers. I'm not sure how she is able to do this, seeing as it has been established that her Val'kyr can only reanimate Humans.