Hidden Worlds of Warcraft

1Up has published a new two-page article entitled "Hidden Worlds of Warcraft", in which they take a closer look at some of the unreleased locations Blizzard has coded into World of Warcraft. A snip:
Looking at the Caverns with a map viewer exposes two of the most complete of the unfinished zones. One of these is a dense jungle that looks like it might be a part of Tanaris in the distant past.

The other cavern exit opens on to what is clearly meant to be the Hilsbrad Foothills at some point not too long ago, before it got beat all to hell. Sights like this make the Caverns exciting to speculate about. They give the developers an excuse to take players to any point in Warcraft's past. Who wouldn't want to see, say, Lordaeron before it fell, or the Sunwell before it was defiled? It opens up a whole world of possibilities.

My vote is that many of these areas will be implemented with the game's expansion pack.