A bit of a bummer that Blizzard's only interested in us fighting the big baddies. I thought for a few minutes of some more down-to-earth lore that I'd be interested in advancing. We could tie in Void Lord stuff as reasons. Note that I have only a passing knowledge of lore, I apologize for gross errors.
Premise: With the legion out of the way, the Void Lords have stepped out from behind the curtain and seek to destroy Azeroth. We are losing, and we need everything at our disposal to fight them back.
We need the aid of the Dragonflights: The dragons are dying off. Quote: "The whelps that resided within the regrown Sanctum were the very last red whelps there would ever be.". But we're friendly with the Dragon Aspects. We're tasked with searching the ruins of Blackwing Lair for forgotten research..is there any hope for the dragonflights? We need their help. We are on the precipice of destruction -- can we resume research into the chromatic dragonflight, no matter what the cost? How will Wrathion react?
Lady Jaina Proudmoore: Varian spared no expense repairing Stormwind from the attacks of Deathwing and the Legion. Yet theramore Isle remains a crater, and Anduin has no interest in making the horde pay for their crimes. Now Khadgar has the ear of the Council of Six and has them twisted around his finger. Who knows what games he is playing?
There's also more race-related lore I'd be interested in seeing.
Night elves: "Night elves are mortal, possibly forever." Think about this: You've been immortal for 13,000 years (Tyrande and the like), but you suddenly lost your immortality. That's pretty huge! Seems like this is something you'd like to recover at any cost! There's been recent whispers in the dark, that perhaps there's a way...
Orc or Trolls or Tauren: The Horde's gotten the raw end of the deal, with leaders dying left and right and the like. The trolls have been decimated and have had to fight their own kind for a long time (ZG, ZA, Zandalari, etc). With the Legion defeated, millions of worlds are now open to them. Maybe there could be a Horde-only part of an expansion dedicated to colonizing a new land in order to rebuild.
Just some thoughts.