"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."
"A handful of ships have ventured from Kalimdor away from the Maelstrom — to the north, west, and south. None have yet returned."
After the Burning Crusade was released and Blizzard were asked to reflect on the reaction it got, they claimed that players actually preferred spending their time on Azeroth, that high or "space fantasy" conflicted with the games gothic tone. With Northrend and Pandaria now complete, the amount of places to visit is now limited to a) the islands of the South Seas (Zandalar, Tomb of Sargaras, possibly underwater zones though the reaction to Vash'jir wasn't exactly positive) or b) some type of sky city in the vein of Vortex Pinnacle or c) the elusive "other side of Azeroth".
Like with Northrend or Pandaria, there's really nothing to see map-wise. Theories have been MORE PANDA MIST, or maybe the Titans didn't want anyone knowing what's there when they built their glittery globes.
Naturally, the next expansion must be Burning Legion themed (I mean, there's only 7 million clues), but perhaps this could be a future one? It'd be a shame to see it Anubarak'd into something small like a SUPER SECRET LANDMASS PATCH with 10 bosses and 200 dailies, but I can't even speculate on what actually MIGHT be there.