1. There's not another whole region on the game card.
2. Unova is nowhere near Kalos, if the location of the real-life regions the Pokémon regions are based on is consistent.
3. Hackers have only discovered two unavailable Mega Evos.
There are probably some in-game events for Diancie and Volcanion (less sure about Hoopa), as there are some in-game hints to them. There's probably not anything else of significance hidden, though. --- Creator of Jay's Journey (see quote!) "It's not ten years old! Therefore, it sucks!" - Nostalgia whores everywhere