Narratively speaking of course.
This expansion has proven the faction disparity has worsened. One way or another the Horde and Alliance are suppose to make up and fight together again.
Will it be under the banners of Horde or Alliance. Who knows.
But one thing is for certain.
Most Horde players will be funnelled along into the Cenarion Circle, Dallaran, Argen Dawn or whatever Alliance themed but neutral organization.
Neutral Organization full of characters like Malfurion, Velen, Khadgar and so on.
So the question is, narratively, how are we suppose to make sense of a Horde character waltzing back to some Night Elf quest giver working for Cenarion Circle or equivalent to protect the World Tree when just one expansion or few patches earlier that same character was complicit for Teldrassil?
The game seems to be indicating absolutely everything is because of Sylvanas and the rest of the Horde is completely blameless or... you know... just mislead.
So its not really their fault.
Do we just ignore everything the Horde player and various Horde racial leaders were involved with?
What is Blizzard going to do to the Horde to explain why Dalaran, Cenarion Circle or every organization like them would allow the Horde and Player PC who burned civilians to death to help them kill 8 mobs or deliver so-and-so package?
Logically wouldn't the Cenarion Circle be hostile to Horde players?