Actually I knew about Hoopa, Volcanion and the Mega [email protected], but Diancie I don't remember to be on that leak; also, as far as I remember, that leak came from glitching, not from ripping the code, so there is still the probability of more hidden Pokémon within the code. But if Diancie was already leaked, oh well. I still hope there are more Pokédex expansions via DLC, even if unlikely.Diancie is in the code. A hacker discovered it back in early November, along with two other Pokémon that you may not know about.I´m not sure whether XY´s code has been already hacked/ripped, but if Diancie is not in the original XY code, then we already have proof that we'll be getting Kalos/National Pokédex expansions within the generation via patches and expansion packs.
Anyways, thanks for the info.