CEO John Smedley took to the official forums earlier this week to provide some details. Not only is SOE working on a second continent (Esamir), but it's got a third one waiting in the wings.
We are working hard on Esamir. It's getting closer and closer to a finished state where we want you guys to play on it. It's pretty awesome and very different gameplay-wise than Indar.Further updates, including performance, gunplay, and spawning tweaks, are all viewable on the official PS2 boards.
After that, Amerish will go back to being worked on. These continents are taking longer than we expected and it's possible we end up launching with two and delivering the third shortly after launch. We're working super hard but we have some resource bottlenecks. We also are going to see how the game plays with two continents before making any final decisions, so please do us a favor and don't judge any of this before you play the game with two.