According to a roughly translated interview with Iizuka, the next Episode of Sonic 4 is going to support 3D. While that is flimsy as hell when it comes to information (which is why I post this as a rumor), it certainly makes sense, if you consider that Sonic Generations does support 3D. Of course, there’s also the 3DS of which we don’t know yet, if the second Episode will come to it too.
[Source: Tssz]