Calling it now. Il Mheg looks like an easily derivable form of "Ala Mhigo" after a few centuries (or millennia) of sound changes. Given the repeated references to time, and Yoshida's cheekiness about revealing where exactly the expansion takes place, I'm convinced that for at least part of it we'll be traveling to various parts of Eorzea in the/a distant future.

Il Mheg of course would be a future version of Ala Mhigo/Gyr Abania. The mountainous terrain seems to match, and it looks kind of like you'd expect after the world has been blasted with way too much light. The Rak'tika Greatwood could easily be a future version of the Black Shroud, although it could also be part of the forest in Dalmasca/Nagxia, or even a part of the world that's not forested in the present.

Are there any place names we know of that could plausibly turn into Rak'tika or Amh Araeng? I'm still thinking we'll explore new areas in the present, but we'll probably have at least 3 zones that take place in the future, and Il Mheg is only one of them.