The people at the bottom of the last two images would make it possible that it isn't a Sonic game. Looks like an RPG.
Though I'd have to argue that people in the concept art doesn't completely debunk this as not being Sonic, the concept art just doesn't feel very sonic to me. you may have something there with the RPG route, whats the common RPGs that SEGA currently has?
The style doesn't look like something from a Sonic game at all, even the more serious ones. SEGA of Japan also has these kinds of countdown sites a lot and they usually end up being A: underwhelming and B: something that won't be released outside of Japan.
Nothing to see here folks, turns out it's some online Korean game: http://www.neogaf.com/forum/showpost.php?p=47418398&postcount=170
