Remember the Mongrel Horde idea Blizzard had for an enemy faction led by Garrosh Hellscream before they settled on the Iron Horde concept for WoD?
https://wow.gamepedia.com/Mongrel_Horde
I was thinking what if they carried this concept into a future expansion just under new leadership? I came up with an idea for a name to give to this faction of various mongrel races: The Dominion. I was thinking what if the Prophet of the Flame took leadership of the scattered numbers of the Druids of the Flame and set up station in the burning remains of Teldrassil (appropriate since they sought to burn down Nordrassil). Maybe they weren't accepted by the new Elemental Lord Smolderon and have been seeking revenge on the mortal races that vanquished Archdruid Fandral Staghelm. With N'Zoth dead and their Twilight's Hammer allies completely vanquished, they now seek out the various "mongrel" races around Azeroth to forge an army of fiery vengeance to take the world by force in a whirlwind of flame and brutality. Each race would take an Oath of Cinder to be re-forged into a being imbued with a Spark of Wildfire, similar to the Druids of the Flame.
Here are some of the races I thought of:
1) Druids of the Flame (for obvious reasons)
2) Gnolls
3) Kobolds
4) Centaur
5) Quillboar
6) Saurok
8) Troggs
9) Pygmies
10) Ettin/Ogres
11) Drogbar/Necrodark
12) Yaungol
13) Magnataur (ironic since their natural habitat is ice!)
I didn't pick any water-based races like Gilgoblins and Murlocs because I couldn't wrap my mind around how that could feasibly work since I integrated this Spark of Wildfire theme for this faction, but maybe you guys are a little more creative in that sense. Any feedback or suggestions would be appreciated!