Like the earlier announcement of an announcement to take place at Jump Festa, we're now hearing about one that will be in an upcoming issue of Coro Coro Comics. Unlike the previous announcement, this one is a bit more specific. We know that it will be for a Pokémon game, and that it's being hyped up. We're due for news on the suspected Pokémon Gray Version, so it very well could be that, but that's just speculation.
Stay tuned for more info as it becomes known.