Though a game is indeed being developed, platforms have yet to be announced.
http://www.nintendoworldreport.com/news/29242
Sonic & Sega All-Stars Racing 2 is in development, an attendant of the New York Toy Fair confirmed to Kotaku.
The game is being prepped for the holiday. Details regarding the new characters, stages and even gaming platforms, however, were unconfirmed. It was rumored that the game would make its way onto the 3DS and Wii U, though it still remains a rumor.
The original Sonic & Sega All-Stars Racing made appearances on every platform, including the Wii and DS.