Back during the Warrior of Darkness storyline, there was mention that there were 13 reflections of Hydaelyn and Zodiark after the Great Sundering as well as just as many worlds to house them. It's also revealed to us that seven worlds have fallen out of balance, not including the First from which the Warriors of Darkness came. Barring events that can be considered non-canon such as the Lightning event and the FFXI crossovers, there are still some pretty solid connections to the other Final Fantasy worlds. One of those worlds specifically is called the Void, which was enshrouded by darkness and has some striking similarities to Final Fantasy 3. Not only does the Cloud of Darkness exist within the Void as a driving force, but she commands the voidsent with which she has been able to terrorize all of the worlds. But how does this connect us directly to Ivalice?
The idea originally stemmed from the realization that Zodiark has only ever existed in games belonging to the Ivalice Alliance prior to Final Fantasy XIV. It also seems to have correlations with the Zodiark in FFXII since the esper in the game is described as having near absolute power, but there is no mention as to how they know this. It's my theory that the Zodiark in Ivalice is in fact a fragment of Zodiark and part of the 13 reflections. This would mean that there's a high chance that Garlemald is a reflection of Archadia and given that the current map can potentially hold the entire known map of Ivalice. It's also very possible that versions of the Bangaa, Viera, Seeq, and Nu Mou exist within the FFXIV universe. Of course only time will tell if this is the direction they choose to take, though it is fun to speculate.
This isn't exactly news to most players though, since even in ARR there were a ton of similarities in both enemy and environment design but everything was circumstantial. It wasn't until Stormblood was released that we received the world map of Eorzea, so use this thread to speculate for yourselves whether or not we'll see something akin to Ivalice when we finally make it to Garlemald.
Known map of Eorzea
FFXII map of Ivalice