According to a mysterious new leak, it seems that three completely new Pokemon are set to release via future events in Pokemon X and Y. Along with the leaked information, the person also posted an image of the three new Pokemon. These include a Rock / Fairy Pokemon called Diancie, a Psychic / Ghost Pokemon called Hoopa and finally Volcanion, who is a Fire / Water Pokemon.
While I remind you this is just a rumor, the images do look authentic. In addition to that, this might explain why the guidebook lacked a Pokedex. This has been speculated in the past, so it is definately something to consider.