According to Sonic Stadium, an anonymous tipster has spoke to Sumo Digital, who developed Sonic & SEGA All-Stars Racing and F1 2011, that a Sonic & SEGA All-Stars Racing could be on the way. The source claims the developer said this:
“Now working on another title for Sega on 3DS, VITA and WiiU. [The] title we are working on is top secret but the last game we did for them was Sonic And Sega All-Star Racing, so the logical conclusion would be… ”
This is pure speculation, and has yet to be confirmed by SEGA themselves.