http://images1.wikia.nocookie.net/__cb20090401054320/ffxi/images/6/63/CompleteWorldMap.jpg
2 continents. That's all we have explored so far, not including the past areas. We still have the Great Southern Empire and the Far West Continent. There's also the Far East that is connected to Aht Urghan!
I'll also point out the Orc and Gigas homeland to the far north that could be connected to major events that could happen in the future.
If you think about the world map and compare it to Earth, there are many cultures left to explore in the world of Vana'diel.
The Far West could mimic a more early-American land of forests and mountains, filled with new kinds of enemies such as Bison and Bears.
The Far East could be a more Asian-like culture with it's architecture and landscapes as well.
The far South could be more tropical much like Kazham, having more Rainforests and having culture similar to Africa or South America.
There's just so much left that could be done with this game. I honestly hope more innovative ideas can be made and more areas can be explored with new stories left to be told.