I just watched part of a video of someone talking about how much they, and all other Pokefans, want a Pokemon Snap 2. I wanted this, but then I realized that X and Y could have a Snap sidequest or minigame in it.
I was originally thinking that there would be a safari zone-type place, but you just take pictures, but then I remembered that there are many different places to go to in Pokemon Snap. There could be multiple places to go to, or just a separate island to visit, similar to the island in Snap.
Or it could be the way you expand your Pokedex, by taking pictures mid-battle and upload them to your Dex. If you forget to, then it won't be added.
This actually makes sense because in other games, there hasn't been a Pokedex before, so you go to fill it up, and somehow a picture of the Pokemon MAGICALLY APPEARS, even though the Pokemon has never been catalogued.
Also, while typing this I remembered that the first Gym Leader is a Photographer.