This info comes straight from the mouth of three GM’s, so while I have no “official” statement from a Blizzard rep (I don’t have any sources inside Blizzard, just a few GM’s that work for them, looking after WoW and battle.net) it should still be considered solid information as all three have seen multiple new areas and are just part of a “plethora” of testers that Blizzard has in these new zones.
The first of these expansions has something to do with the Emerald Dream, as there are currently seven “rather large” zones that are related to the Emerald Dream. These are already “fairly fleshed out” with plenty of quest NPC’s and content. The zones themselves are a lot “greener” than anything previously found in WoW, with many “giant” flowers, trees and lakes. My sources said “think Zangarmarsh, but greener, and with much more foliage. The giant mushrooms are replaced with giant flowers, fields of green, and plenty of foliage.” The creatures in these zones are mostly "animal like" at the moment.
Next up there are a few zones that are in “very early” stages of development. The strange part is that they are in no way connected to either the Emerald Dream or the content that Blizzard is working on for the Lich King expansion. These zones are more “Waterworld themed” (Waterworld is an older movie starring Kevin Costner. Look it up.)
There is a zone that contains a “barely floating city, surrounded by a huge body of water”; there are quite a few more “graphics for ships, with big galleons here and there”; and finally there is a new “giant sea creature”. However nothing in these zones is scripted and they are just walked around in for the moment. The sea creature can already be spawned; then again it can be spawned in any zone as long as the command is known, even in good old Azeroth. There are also a few more “Waterworld” based zones out there, but they are not yet populated or finished.
My sources believe that Blizzard is working on the next two expansion packs to the game. One themed on the Emerald Dream, and the other on what looks like “Waterworld”. I have no release dates, however the three commented on how they “have to be done with a few zones by July 2009”. Which puts one expansion pack on track for late 2009, early 2010.
I have no other knowledge on what else comes with the expansion, but one can assume that we will get a higher level cap and more skills.