personally I hope It isnt released for a long while. I played sonic four and felt dissapointed with its numerous flaws mentioned by fans, so It would be a good idea to hold it off for a while, but another reason I think the game should be stalled is because of sonic generations. I played the demo on ps3 and felt very dissapointed with both the controls, platforming, and music. Honestly I dont think sonic team should continue with 2d sonic games untill they can adjust to modern day controls.
Due to the reception of that game meaning part 1 I think they kind of swept it under the rug for now, I am sure they will release a part 2 eventually. But I am also in the camp that believes a large part of that development will depend on how well generations is received.
I think its a good thing they didn't rush part 2 out, they need time to polish the game a bit more.