That track doesn't appear in the Warcraft III, World of Warcraft, or Burning Crusade soundtrack lists at all. Warcraft 2's soundtrack was released as mp3 tracks by Blizzard, and Northrend doesn't appear there, either. So unless this is an old midi track from Warcraft or Warcraft II, odds are that we're looking at a brand new piece of music, and that players will be headed to Northrend very soon.
Now, of course when you think Northrend, you have to think Arthas. Blizzard has said in the past that a full raid of level 80 players would be needed to beat him (at least), so if we are going to Northrend in the next expansion, we may be looking at yet another 10 level cap raise. Then again, just because Northrend opens doesn't mean the cap is going up yet. And of course, even if we do go to Northrend, there's no guarantee that it will be the only new land in the expansion, so you Emerald Dream dreamers can still hold out hope.
But I'd bet dollars to doughnuts that at some point during BlizzCon (my guess is still during the opening ceremony), we're going to hear more about the big continent to the north.
