So is the hypothetical 'Z' ersion people have been trolling about for the last five pages!
Not when you consider it's very likely that there will be another Pokémon in the game that would likely "represent" Z, but sure, it could not happen, and this could all be brand new and different, so we'll see.
I'm not talking about any games after Pokémon X and Y, I personally am referring solely to the possible 3rd member that is related by theme in some fashion. Unless it becomes DLC later on, there should be a 3rd member within the games that shares a theme, but not it's not confirmed, just likely.
I'm definitely looking forward to the Legendaries in this game. My wife has already claimed whichever game gets the deer because it resembles the guardian from Princess Mononoke. I also like the design of the Y-bird. I am curious as to what the additional legendaries would be based on the theories that are being thrown around.
I've heard people referring to X,Y, and Z as being reference points in the 3rd Dimension (3DS), so I'd be curious to know if there would be possibly a Legendary version of Porygon-Z.
I've also heard people refer to X.Y being DNA chromosomes, so I'm curious to know if maybe Deoxys might be obtainable in game without an event. Or maybe we'd come across the meteor site where Deoxys landed. Then of course in that regard, we've also been introduced to the DNA Splicers in Gen V, so maybe we'll be introduced to spliced legends.
I'm pretty sure Porygon Z exist solely because it's a corruption of Porygon 2 hence Z and 2 look similar in appearance.