Zandalari Isle is an island shown as part of a rough map during BlizzCon 2011 to the north of Pandaria. As of Patch 5.1, it has not been seen in-game. However to add confusion, Patch 5.2 appears to be introducing 2 new islands north of Pandaria, the Isle of the Thunder King and the Isle of Giants.
The island presumably is or was the homeland of the Zandalari. Is this the ancient land of Zandalar? Likely not, since a troll leader encountered on the Isle of Reckoning, off the northeast coast of Kun-Lai Summit, appears to indicate that Zandalar may have been destroyed in the cataclysm.