What mythical being (not represented in Warcraft) would you like to see represented in-game or in-lore?
Personally I would be interested in Blizzard's take on some Japanese mythical creatures considering that Kaldorei are at least partially based on Japanese/Shinto culture. One race that I think that could fit into WoW really well would be tengu as an alternative bird race to harpies or arrakoa
Maybe make them similar to worgen, descendants of night elves transformed by druidic magic.
Merfolk are another race that could be interesting, especially with the idea of a South Seas expansion. Interestingly enough in Ulduar, images of merfolk are depicted on the walls.
I could imagine merfolk in Warcraft being descendants Titan constructs designed to shape the waters of Azeroth alongside sea giants, being affected by the Curse of Flesh.