My theory (based on recently playing through Horde side of the scenario) is that the reason why this has never happened, and will never happen even in Midnight, is because in Blizzard´s eyes, they really did nothing wrong.
We players have the tendency to look at what we see and analyze it to death. Sunreaver NPCs have click-on option that mentions SC mugging them, capturing them even though they seem to have no idea some Sunreavers aided the Horde and betrayed Kirin Tor. Single SC NPC is keeping a Sunreaver Agent over water with shark in it and drops him when attacked. Alliance troops attacking Sunreaver NPCs in the streets. Jaina murdering people in the streets (although this is something I´ve not seen in current version, she attacked an NPC, fought it for a while, then TPed it away, which made me feel like this really is the result of some janky NPC behavior where Jaina and Sunreavers aggro each other and it takes some time for her scripted “TP them away” thing happens, resulting in some NPCs dying because she killed them too quickly). All these things, to someone who tries to only analyze what they see will paint an unpleasant picture of the Alliance.
The problem is, Blizzard doesn´t seem to work that way. Purge of Stratholme, probably the most discussed event in Warcraft´s history, where people to this day argue whether Arthas was right, is actually very simple from perspective of Blizzard dev who made the mission: Arthas is evil, Jaina and Uther are right, and by the way, Arthas doesn´t even finish the job, he leaves many people alive and doesn´t burn the corpses to prevent them from rising because he just doesn´t care (those people are then the ones you see burning the corpses). In fact, Arthas helped the Scourge because if you kill people, Scourge can raise them as ghouls.
https://www.youtube.com/watch?v=4tigJUxQmJs
(for those who don´t believe me, yes, it´s an insane take, but I´m not making it up)
The point is, where we see moral complexity, Blizzard often doesn´t (and where we see dumb storytelling, they often see stroke of genius). Given how Aethas behaves in his Trading Post bit, how Hathorel is on the “bad” side in BfA, and how Sunreavers have to work to be let back in during Legion even though Kirin Tor lets Horde in earlier, makes me think that to Blizzard, the story has clear villains and they definitely don´t wear blue.
Now, why this might be, my (game) theory is that this might have always been the intention. Sunreavers helping with Divine Bell extraction in Darnassus is one whole part of 5.1 Horde questline. However, SC actions in Purge tend to be shown through click-on text or behavior of NPCs (some of which was even said to be a bug). We look at these things and paint the picture of the events without attributing greater importance to one or the other. But to Blizzard, Sunreavers using Dalaran to attack the Alliance might have been huge plot point that they crafted as part of the story they wanted to tell, while click-on text in Purge was left to some intern who just made up 5 sentences that NPCs say when you free them.
The problem of Blizzard is that they tend to look at their intent and base their lore on that rather than what made it to the game. The most stable dev mentions that originally, Stratholme humans didn´t turn into zombies if Arthas found them, but players didn´t like killing innocents, so it was changed that they always turn into zombies automatically. He doesn´t realize that this paints the picture of everyone in Stratholme being infected and doesn´t understand why people think that´s what was going on.
Just like, IMO, Blizzard devs in past few years don´t understand that to many players, Purge of Dalaran is one of those rare situations in lore where Alliance was portrayed as doing bad things and that, while Sunreavers aren´t innocent, they aren´t the villains of this story.
Also, first comment, yay!