There is SOMETHING on the other side of the world, there's bits and pieces of it spread out over the lore of wow, but what I can remember is that people have ventured there and never returned, mysterious eh? So there might be a whole continent on the other side, but im pretty sure that I read some where that it was a vast ocean with giant sea creatures, might be mistaken tho, I will try to find a link in a sec...
http://www.wowpedia.org/Azeroth_%28world%29
"The world of Azeroth also has lands located at the other side, beyond the Veiled Sea to the west of Kalimdor, and beyond the Forbidding Sea to the east of the Eastern Kingdoms. No one is sure or has knowledge of what kind of creatures, lands, cultures, life, and sentient being lives in the other side of Azeroth. It is clear though that it is very dangerous. "
There we go