Game Freak's official website has posted this strange image, accompanied by the text "This classic game played all over the world will be reborn from a surprise collaboration." While the horse-like image could be from Rare's Viva Piñata (To which Nintendo recently acquired the rights), the "collaboration" could possibly be with Pokémon, seeing as how it has played an important role in Game Freak's history, not to mention it's also "classic." All this is just speculation and the image may not have anything to do with Pokémon at all.
Ah, what a grand day, indeed. We present, Solgaleo and Lunala, the two newest legendaries in the Pokémon universe. Solgaleo (as seen on left in picture above) will star in Pokémon Sun, and Lunala (right) in Pokémon Moon. Both look like they could deal out a massive whooping on lil Popplio. Here's the new trailer which features the legendaries, as well as new gameplay footage, and a look at the new Pokédex:
In Sun and Moon all players will get a Pokédex inhabited by the ghost-like Pokémon Rotom, who can possess/inhabit objects and machinery.
“It does much more than record Pokémon info—it sparkles with its own personality. The Rotom Pokédex shows your current location and your next destination, and it also gives you advice on where to go next, based on the conversations you have with others! It’s likely to be of great help to you in many parts of your adventure.”
Lastly, here's a detailed look at Aloha: the Hawaii-inspired region of Sun and Moon: