Well yes, that's exactly why I hate the attempted pushing of factions in 2017's Warcraft universe.
We're seeing time and time again that the Horde and Alliance need to work together. We're seeing that the conflicts come from stupid misunderstandings and maniacal leaders. We're seeing that both factions are inherently good and sometimes do bad things.
And yet what are we doing still? Being forced into these idiotic faction conflicts that do nothing but pull the story back and kill any feeling of character progression that the leaders may have. A good example was how Jaina treated the Horde player in Warlords of Draenor. Granted, I hated that expansion, but I loved how she went from outright hatred to simply cautious wariness in the wake of the Siege. She's not willing to go full on "get the fuck out, screw you Khadgar" and even helps the player during the legendary ring quest but doesn't hide the fact that she'll be watching you carefully.
Fast forward to Legion. Hey, look at that. The factions have once again regressed into conflict. And then we see again that the unification and neutrality of the Kirin Tor and the Order Halls, with the combined forces of our new allies, is actually succeeding in pushing the Legion back. This feels like a pretty good direction for the story to go from the beginning, and would be if we hadn't seen it like five fucking times now.
Are the Alliance and Horde ever going to stop killing each other during the literal apocalypse? Are we ever going to witness these two factions grow a mutual level of respect for each other? All the repeated wars do is remind me and every other player that both factions are utterly useless and self-destructive, which is why I hate when they force you to be a military leader of them or act as if you should be proud to represent their shitty priorities and warmongering over misunderstandings.
Alliance got punished as well for blizzards writing??? It would just be fair to give the other side a "fuck yeah, take that shit" expansion as well.
Yes the neutral targets would be dangers native to the area. You also don't have to create the dungeons twice. Just replace the horde mobs with alliance mobs and VV. The abilities obviously would be the same. (e.g ToC faction champions encounter)
What is this "area" we would be going to? If it's a faction war xpac, wouldn't it make more sense to focus on the old world? If you would just change the mobs' faction, what's the story behind the dungeon anyways, considering most dungeons these days are sort of a capstone to the zone's story. Would you just tell two different stories to Horde and Alliance? Then you have a problem telling your playerbases which one's are the canonically true ones.
The Kirin Tor definitely have a history of being partisan, but I think Khadgar is mostly neutral and willing to work with anyone who shares his goals regardless of faction. He was after all the primary influence that forced the Kirin Tor to drop their pro-Alliance stance and permit both the Sunreavers and the Horde to return to Dalaran.
"We're more of the love, blood, and rhetoric school. Well, we can do you blood and love without the rhetoric, and we can do you blood and rhetoric without the love, and we can do you all three concurrent or consecutive. But we can't give you love and rhetoric without the blood. Blood is compulsory. They're all blood, you see." ― Tom Stoppard, Rosencrantz and Guildenstern are Dead
I can see it now:
When faced with the new playable faction, 'Remnants of the Legion' comprising all the main demon races, the Alliance and the Horde permanently join together under the banner of the Alliance, with Anduin and Sylvanas as joint Supreme Commanders.
Individual races need better representation in game regarding why they are in their parent faction and what grudges/conflicts and animosity they have with rival races and factions.
The game is in a constant state of change. We need this reflected in game.
Stronger identity and purpose for each individual race
expanded reasoning for faction as a whole