Funnily enough you can still hear Horde-warfront-music playing in the Southern Barrens at several spots. Here’s a video (as a sidenote the music makes the entire zone even more epic, considering that it’s already one of the best “battlefield”-zones between Horde and Alliance in the entire game):
The BfA-trailer also has a completely different tone when compared to the ingame-events. Sylvanas is able to actually rally the Horde behind her, Greymane talks about how Lordaeron will be theirs. Funnily enough the trailer also works better with statements made by Blizzard before the BfA-release. One of such statements was that Anduin launched the attack in order to “prove himself”. Well, that is not really the case ingame as the entire attack is more a counteroffensive to remove Sylvanas from power.
Something must have gone horribly wrong behind the scenes, because you cannot tell me that everyone was completely fine and cool with a complete rehash of Mists of Pandaria. This could also be the reason why Aszhara and N’zoth feel so tacked on.
And if we look at some of the datamining: Nearly all warfronts after the initial ones took place in Horde zones. Quel’Thalas, the Barrens, Aszhara. It really feels like originally the Alliance would have been far more aggressive and pro-active in their approach against the Horde. This can be tracked be even further to 7.3.5 with SI:7 openly attacking goblin miners in Silithus or even Stormheim where its the Alliance who shoots first. A somewhat unique move from the usually defensive and passive Alliance.
Continuing the thought and now speculating: Maybe one of the original ideas was growing militarism and warmongering tendencies within the Alliance. Maybe with things like the Alliance military becoming a state in a state and overruling Anduin, launching offensive actions against the Horde. And for one the Alliance would stand at a crossroads having to choose between a more peaceful or militarisic approach. The Horde meanwhile would, for probably the first time ever, be in a defensive role.
Funnily enough both factions would probably be far more happy with such a scenario: The Horde has finally good reasons to fight, while the Alliance would be happy that they can finally go to town against the Horde and smash some faces in.
Edit: The more I think about it the more things start to fall into place all throughout Legion and even in some moments in BfA. I’m gonna have to write a complete post about this.