There are three zones not revealed in the in-game Azeroth Continent map. One is west of Burning Steppes, the other one is east of Burning Steppes. They are as big as Deadwind Pass or bigger.
Another area is east of Grim Batol(Wetlands). There is a large patch of land from north to south: covering a height from Eastern Wetlands, Loch Modan, down to Badlands. Hopefully future content. The land to the East of Wetlands could be accessed openly through southeastern Badlands until patch 1.9—where access was blocked. The area was pretty large, but there was no content there and lacked textures.
Western Burning Steppes
The land west of Burning Steppes seems to have two entrances. One is through the right-side – uphill – of Black Char cave in Searing Gorge and the second entrance is near the Altar of Storms—northwestern Burning Steppes. Once you walk into both entrances your character is blocked by an invisible barrier.
Eastern Burning Steppes
Rumor is the new Burning Crusade Alliance Race’s starting location could be there. If indeed the Draenei becomes the new Alliance Race, this placeholder would be the logical choice. It is just northeast of Swamp of Sorrows where the Draenei of Azeroth lives at.
This section will be updated as new info of World of Warcraft: Burning Crusade becomes available.