Choose who you think would be the ideal racial leader. This is pure fantasy so you are not bound to timelines and death. Just try to imagine the cream of the crop all in current WoW leading their respective races.
Horde Warchief and Orcs racial leader: Grom Hellscream
We got a glimpse as to how Grom might have led the Horde when his son did. People like to glorify Grom, but AU Grom, for better or worse, showed Grom was not much better than his son as far as being a warmonger. HOWEVER... I'd like to think MU Grom might have done things differently, and I would love to see Grom sitting in Grommash Hold with Thrall as his advisor to reel him in.
Trolls racial leader: Zul'jin
He's just the most badass troll ever, in my opinion. I know, he hated blood elves, but we know Blizzard ramped that up just to turn him into a raid boss. For the survival of the Amani trolls, Zul'jin would lead an united troll empire as part of Da Horde under Warchiief Grom, one-eyed, one-armed and all in all his badassery.
Tauren racial leader: Cairne Bloodhoof
Let's pretend it was Baine, and not Cairne who died in some sort of honorable duel to prove himself to his father, and we would have never gotten the Baine we had, but kept the greatest Tauren that ever lived. Enough said.
Undead racial leader: AU Ner'zhul
I am way thinking outside the box here, so bear with me. Sylvanas' fate unravels as it's supposed to. Garrosh'ed, exiled, becomes Goddess of Death, or simply its puppet, what have you. The Forsaken need a leader. Who does Grom turn to? Perhaps one of the darkest casters he has ever known, and where does he get the body? Alternate Draenor. With the Forsaken's identity no longer tied to Lordaeron, they are now represented by a council led by Ner'zhul. This is due to AU Ner'zhul's gross underuse in WoD.
Blood Elf racial leader: Kael'thas Sunstrider
We all know he went mad for no good reason. It should have never happened, and I still yearn to see what the Kael'thas of Warcraft III would be like leading his people in a post-Lich King Azeroth.
Goblin racial leader: Gallywix
He is perfect and does not need to be changed!
Pandaren are such a non-presence, I don't feel the need to appoint two racial leaders that would make much difference.
Obviously I won't include fantasy allied racial leaders as it's a relatively new concept and they're just alternate flavors of their main counterparts.
Alliance High King and Human racial leader: Varian Wrynn
Everyone knows killing Varian was the biggest mistake of Legion and it served no purpose. Anduin should have died instead, and it would have been the noblest thing he ever did. Alliance keeps its flawed but great war hero and Anduin becomes a legend instead of an annoyance.
I would keep the Council of 3 Hammers, I like it.
Night Elf racial leader: Illidan Stormrage
Enough! The night elves will no longer be a joke! After Tyrande and Malfurion die an agonizing death, the night elves seek out Illidan, the savior of the cosmos and jailor of Sargeras. The night elves begin a new chapter, weaponizing the fel from the knowledge Illidan imparts by plucking Sargeras' toe nails one at a time. Tree huggers need not apply. Druids accept this new destiny, expanding their ranks with fire druids and fel druids who can shape shift into animal demons and fel trees who run around with fel flame on their burning bushes.
Gnome racial leader: Gelbin Mekkatorque's Head
During the process of becoming a cyborg, a tragedy occurs; only Mekkatorque's head and brilliant brain is salvageable, being placed in a cybernetic spider walker. As the mind of the alliance, and now simply a head, he begins inventing twisted machinations to aid the alliance in crushing the Horde.
Worgen racial leader: Tess Greymane
When her father is killed in combat, Tess leads a joint effort with Varian to re-take her father's land, contracting the Worgen curse and reclaiming Gilneas for the alliance. She's going to be a badass worgen in tight leather pants and introduce Bards to the Alliance: rocker edge lords who use guitars to blow out their opponents' eardrums and buff their party with wicked guitar riffs.
Velen remains leader of the Draenei.
Imagine all of these ingredients boiling in the same pot of modern day Azeroth, it sure would make for a better faction war. I dare you to fantasize better.