Gnolls and Furbolgs don't really fit Alliance aesthetics. They'd easily fit the Horde, though.
For the Alliance, I'd retcon the Centaurs so that you have a chivalrous tribe of them (maybe have that tribe located in the EK if you want), with the cannibal tribe that hunted Cairne being the exception to the rule. Would fit right into the Alliance's classical aesthetics.
There was the
The Rise of the Horde novel. In that novel the Draenei were presented as farmer village folk who got easily slaughtered by the Horde, which lends an undertone of irony when Grom claims that they were glorious conquers, and explains why the Horde collapsed when they came into contact with the Alliance, as they had never actually fought someone actually strong before. Ofcourse, that makes no sense with TBC's retcons which made the Draenei a spacefaring race with shield generators and lasers who should have easily repelled the Horde.
The Rise of the Horde book details some atrocities the Orcs committed against the Draenei but I don't think the Path of Glory existed before TBC.
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Also this.
I've gone more indepth in the "how would you redo WoW's factions" thread. Either make the Night Elves their own faction, or don't make them playable at all. Forsaken have other complicating factors.
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The story ended in Northrend. The Alliance and Horde's story was completely finished by the end of WC3. The Alliance and Horde had rid themselves of each other and were at peace. The sequel to WC3 is TFT, which noticeably does not feature the Horde or the Alliance at all (they got a shoehorned in bonus campaign). The story of TFT was about Illidan's attempt to destroy the Frozen Throne. TFT ends on a "to be continued" with Illidan dead and Arthas donning the Lich King's armor. If you were to write a sequel continuing from TFT, then the very basic outline would be that Kael'thas takes control of Illidan's forces and makes a retreat, regroups, and plans his next move. Kil'jaeden finally shows up. Kael'thas and Arthas might make a temporary alliance to fight against him. The Legion is repelled, and then Kael and Arthas turn on each other. You could write the Alliance back into the story with them arriving to help Kael'thas kill Arthas, avenging Lordaeron and eliminated the Scourge menace. I don't see any way to write the Horde back into the story as they have no stake in the conflict.