User blog comment:Bowser & Jr./Generation VI of Pokémon confirmed; Pokémon X and Pokémon Y announced for the Nintendo 3DS/@comment-1518158-20130108233937/@comment-2072003-20130109000557

Let me make this statement. X and Y are two of the three coordinates in a 3D plane and the third coordinate is Z, so I guess they could make a third version if they wanted to (although I hope that it's more of a sequel like BW2).