WoW Insider have created a short, concise list of what we can most likely expect to find the expansion on when Blizzard hopefully announce it at Blizzcon.

• Obviously, there's Northrend, which contains 13 distinct regions,
• then there's the South Seas, 5 islands located off the southern coast of the Eastern Kingdoms (and include Zandalar, which I must note already exists in the game) -- on one of these isles you'll find the well-known Goblin city of Undermine,
• then there are a number of other islands located in the Great Sea: Kul'Tiras, Tol Barad, Crestfall, Zul'Dare, Dragon Isle, Balor, and Pandaria,
• the Emerald Dream, which could be as large as Azeroth itself.