On Feb 8th Sega's Associate Brand Manager, Ken Balough announced Sonic 4 Episode II is in early development. Ken Balough later said:
"[....] I can tell you you are going to see new zones that look really cool.
Re-hash kind of depends on how you look at the topography. I mean; we've gone to a lot of areas - Underground mines in Sonic 2, Deserts, Lush green hills, Jungle, Cities, etc.
But yeah - the idea is to introduce new zones with things you haven't seen."
Ken also admitted that Sonic 4: Episode 1 had aspects that "could have been done better"
Ken also assured that "you definitely wont have to wait years and years a la Duke Nukem Forever."
Tails was also hinted to be in the game, thanks to Aaron Webber stating:
"Aristotle, often cited among the Greeks who wrote about Hedgehogs and their powerful wind-sensing abilities, was himself later categorized among writers and thinkers in a comparison that any Sonic fan might find quite interesting. Rumor has it, in fact, that there are two styles of science: compared as either objective or abstract. Find the false line within this paragraph itself, and you may find hidden answers of your own."
Which, when putting the clues together, refers to the essay "The Hedgehog and The Fox"
What we now so far:
-It's in early development
-The game promises new "cool" zones that we've never seen before
-Tails is said to be in it
-It's supposed to improve on Sonic 4 Episode 1's faults
-We won't have to wait forever until it's out