Mists of Pandaria
MoP This section concerns content exclusive to Mists of Pandaria.
After discovering that Sunreavers helped Garrosh Hellscream steal the [Divine Bell] by using Dalaran portals to infiltrate Darnassus, Jaina mobilized the Kirin Tor, Alliance forces, and the Silver Covenant to purge the Horde from Dalaran. Though Aethas Sunreaver claimed he knew nothing of Garrosh's scheme, Jaina nonetheless chose to incarcerate him and his Sunreavers after Aethas refused to order his people to leave the city peacefully. Those that surrendered were imprisoned in the Violet Hold while those that resisted were put to the sword, after which Jaina pledged the Kirin Tor to Varian's war cause, effectively bringing Dalaran back into the Alliance. During the purge, Dalaran had already left Northrend and is now in motion. However, for game purposes, Dalaran remains unchanged after the questline is completed (see Notes).
So we should, I think.. Gameplay wise, see actually that the Dalaran city is within the Alliance, somewhere\whatever place it should be in Azeroth.
It doesn't matter if it's in Dalaran for Horde and Alliance, while it's just for Alliance somewhere else in Azeroth.
Because it's past time, you are currently fighting the Scourge when you go to Dalaran in Northrend.