Update: Decided to adjust a couple of things. First the message seems to more specifically say that a new Sonic project is coming next year (project seems to be the prevailing word rather than game, but some do report it as a game). While it’s not specified to be the big anniversary game, it is said that details will be announced at the 25th anniversary party in San Diego on July 22nd. The event in San Diego will also be live-streamed via Twitch. Finally, another very reliable site has put up the full details, along with the link to the live-stream archive which you can see below.
Original: The second key thing, again from Joypolis, is that Sega have confirmed that the next main Sonic game is indeed due in 2017. No other details were given at this time.