It's neither been confirmed nor denied, but I'm hoping for a new Sonic Adventure title next year. The Chao in Space short seems to hint at one, since Sonic Team only commissioned shorts like these previously to hype up new games. I don't see why they'd build up SA2 hype if they weren't going to make a real Sonic Adventure 3 (none of that '06 boost formula nonsense), or possibly even remake SA1 and 2 similarly to the Crash and Spyro remakes.