According to Serebii: It seems this could very well be the Pikachu and Eevee game news we've been expecting, which was heavily rumoured to be released BEFORE e3. However, this could be something entirely different. Do bare in kind that Zeraora is officially announced now, so there's not really anything they can announce from those games. However, a "new story begins" could mean the anime or a new movie.
yeah im not so sure i'd get hyped for it be a new game entirely, at least something entirely different from the lets go pikachu and eevee that were leaked recently. if this is the pikachu and eevee game, im curious to see if they'll show any early trailer footage of how the game works.