Sega has announced in a recent interview that they aren't planning to release the second episode of Sonic 4 until some point next year. the original came out towards the end of 2010.
"This year, 2011, is the anniversary, so we're focusing on the celebration title," said Sonic Team's Takashi Iikuza. "But moving forward to 2012, Sonic will still be going, so I'd hope to provide Episode 2 then."
This will come as a disappointment to fans who were hoping to see a continuation of Sonic 4 not long after the release of Episode 1. Now it looks like they will have to wait well over 12 months between Episode 1 and Episode 2.