Square Enix has hinted that it’s unlikely we’ll see Kingdom Hearts 3 and Final Fantasy XV released around the same time.
Kingdom Hearts series producer Shinji Hashimoto explained the situation to IGN:
So at E3 this year we announced Kingdom Hearts III and Final Fantasy XV. Both have Tetsuya Nomura as their director, so we can’t create these two big games at the same time.
It’s a difficult job, as we want each game to be perfect in terms of quality.
Since Nomura is involved on both games, hopefully Final Fantasy XV will be out in 2014 while Kingdom Hearts 3 comes out in 2015. Considering Final Fantasy XV is essentially Final Fantasy Versus XIII, the game should have been out already.
Both Final Fantasy XV and Kingdom Hearts 3 will be available for the PS4 and Xbox One consoles.