The Sonic Dimensions rumor is a hoax.
We heard a rumour about a game known as Sonic Dimensions coming to the Wii U. It sounded all kinds of amazing, but now, when asked about the rumour, Takashi Iizuka of SEGA responded with:
Iizuka: Sonic Dimensions? [Laughs] I think it’s a complete hoax. [Laughs]
And while I’m all for conspiracy theories, when the producer for a game development company straight-up says something is fake, it usually is fake. The inverse of that is, if they say one rumour is fake, then respond to other rumours with “no comment” you can be fairly sure there’s truth. In this particular case though, it does seem like the rumour was a hoax.