In an e-mail that they've sent to Destructoid, we can see that Sega is planning to unveil a brand new AAA game at this year's Gamescom.
On top of that, the company is planning to promote Sega Mega Drive Mini and all 42 games will be playable with a "giant fully functioning controller". We will also get a Catherine: Full Body demo (with all cutscenes included) as well as the opening chapter of Two Point Hospital.
We have no idea what this game could be at the moment. It doesn't seem like they will announce a new Sonic game although we do know that they are working on it, so....who knows. Let's hope for the best!