I think we can all agree the Orc Heritage quest has raised the bar.
There are essentially 4-6 heritage armor quests left. (Depending on whether Dracthyr and Pandaren Get Any)
For now, let's focus on Draenei, Darkspear Trolls, Night Elves, and Forsaken.
What do you want to see in these? Lesser known characters elevated to prominence? New plot hooks seeded? Etc...
Here's MY Wishlist to serve as an example...
Draenei: They need to rescue the Broken/Krokul that have been left on Argus's pieces. A trip from Azuremyst to Swamp of Sorrows on Azeroth, to Shattrath and Draenei towns in Outland, to Argus, getting the items needed to create a portal to let them travel back and forth more easily/safely now that the legion is defeated, visiting important places like Auchinodon and such in MU Draenor along the way. Maybe touch on the Ata'mal crystals or the Army of the Light distantly but not enough to leave everyone else confused when that plot picks up again outside the Heritage quest. Velen, Nobundo, Akama (Maybe serving as the Lost One rep?), and the Triumvirate of the Hand could all feature.
Darkspear: There's a LOT of potential here. Rokhan, Zekhan (who needs a bit of flavor repair), Vanira, Bwemba, Zen'tabra and Master Gadrin give a good core cast. I'd focus on exploring the Darkspear's history and the role the various gods they worship gave them in surviving it, as well as them setting them up to remain relevant and not just end up the Zandalari's sidekicks. Adding some altars to the Echo Isles for particular gods would be a nice first step as would, playing politics with the Shatterspear, Revantusk or other troll tribes, and definitely visiting Bwom's temple in Nazmir, perhaps doing something with the Zul'gurub gods that didn't feature in recent expansions.
Night Elves: Whew this one is a minefield after the mess BFA and Sl left them in. The Night elves have already had a lot of sad things said about Teldrassil, WotA, and their past in General. The nelfs definitely don't need more Sad/Pitiable quests lamenting WotA or the loss of their immortality. I'd suggest framing it as a reunification of the Nelfs three pillars of society. Elune Worship getting more detail, along with an exploration of what makes nelf arcane magic from the Highborne unique in a world where everyone's been innovating on Highborne teachings for centuries, and of course what makes nelf Druidism unique now that other races are picking it up. Shandris, Mordant Evenshade, and some new or lesser known Druidic characters would be the best bet. Exploring how the night elves are recovering and Thriving in the face of adversity even while spread out all across the world would be a good angle as well. With Malf gone and Tyrande managing the new World Tree seed their race is less centralized command-wise so that lets other characters in all their scattered settlements across the world full of refugees from Teldrassil step up to do something new, adapting faster after 10k years of stagnation, and could also explore closer ties with natural allies reconnecting with them (Furbolgs especially if we're lucky).
Forsaken: Almost as big a minefield as the Night Elves, the Forsaken are in a weird place with the way Sylvanas leading the Forsaken and the rest of the Horde in a genocide of the nelves and working for the Jailor have made her a base-breaking character both in-game and out. The bad writing from SL and years of making her the ONLY prominent forsaken character and the literal face of the faction had left them with a gaping hole to fill. A lot of folks are not happy about Calia (Me, I am not happy about Calia) or Derek Proudmoore feeling they're too soft for the Forsaken or don't make sense for the faction... or enjoy a new angle on the Forsaken... and others are unhappy with Faranel and Belmont or Velonara and feel they've done things too Stupid-Evil for it to make sense with the Horde or to be enjoyable in general, while others love that they still have some 'evil characters' or at least characters with an edge.
It's also painful that the Forsaken have a light caster on the council but don't have a Cult of Forgotten Shadow member (and that Blizz made the Cult of Forgotten shadow rep a live human)
Simply put, the Forsaken quest is going have to be about finding a way to balance what the playerbase wants, compromising between folks who want cackling evil and folks who want DARK but not so evil it alienates the rest of the Horde... and folks who want whatever is going on with... Calia.