The removal of Naxxramas from EPL forces Blizzard into a serious problem. Somehow it must cause a contradiction and Blizzard must either pick one or leave Naxx where it is and make a second one.
From what quests indicate, players and NPCs were gathering resources for an assault. Perhaps it is better called a counter-attack, since the fortress was seen floating in many places dropping troops. Either way, the stage was set for an attack. Did it happen?
It did. Even more, Kel'thuzad and the many horrors in his fortress were defeated. Perhaps they can come back, but nevertheless, they were attacked and beaten closer to a proper death. This clearly happened before the citadel moved, implying that time has passed.
As we've seen with Kael'thas, people do not exist in the same places at once, instead our characters are moving through time as we change location. Whether or not we have defeated him in TK, by going to MgT we are moving to a time where he was defeated. This means that Naxxramas must be above the Plaguelands even if it has later moved to Northrend.
But what if it didn't? I hope you've read 1984, because we'll have some double-think coming up. Is that what Blizzard plans? Naxxramas was never above the Plaguelands, it was never invaded, no one has defeated Kel'thuzad. Is Blizzard going to act as if the past never happened?
There must either be two Naxxramasi or Blizzard must pretend that the events of a year and a half ago were just an illusion, that Naxxramas was never attacked and that Kel'thuzad was never defeated. It's one thing to recon a story, quite another to retcon our experiences.