As far as I'm aware Game Freak don't deal with spin-offs, if it was something like Rumble Blast 3, Stadium etc it would be by someone else, that's why this announcement could be big because Masuda is appearing alongside Shigeki Morimoto who are both highly involved with main games.
^ That's what I figured. I mean it would be one thing if it was just a general announcement but, with Game Freak being the main advertising(correct me if I'm wrong) for this announcement, I really see it being main game related.
They've done all of the Gen V events and the Genesect event was recently publicized so I think we can rule out a Wi-Fi event. I think it's going to be a game but I'm clueless to as to what game(s) it will be.