Thoes are the four Islands that are aswell called "Echo Isles" On the North-Eastern one, if I am correct, is the Tomb of Sargeras, at the South-eastern one, is Maiev's Landing., south-west is the Abandoned Naga Base. and middle, should be merceneries and others of the sort, North-West should be mystery, I though they're three, or atleast in Wc3 they make the two top Isles into One Big Naga Base (Plus the Tomb of sArgeras)
Basicly, I believe this will be implemented at (if) the Expansion of The Burning Legion, aka, Argus.