Are you kidding me? You've been talking about how the new things they've come up with are apparently "terrible" and you want us to just walk back to Northrend and fight ANOTHER Lich King? That's...awful. There's no way around it.
Thankfully, they know that, and that's why when they have us revisit old areas, there's an entirely new direction and conflict going on. Just because you don't like Pandaren or Pandaria, doesn't mean it doesn't mesh into the story. Also, I don't see you complaining about Draenei, when the playable Draenei had even less representation before their appearance than the Pandaren.