I hope Dimps doesn't have anything to do with the 3DS version because, People bashed the Sonic Generations 3DS version because it wasn't "nearly as good as the HD versions" (which is stupid, Gens 3DS was great IMO). Not only that but Sega also said they were changing Sonic's gameplay up after Sonic Generations, so it's possible for Sonic to no longer have the Boost formula (Rush, Unleashed, Colours, Generations.) Then why would Dimps still be the creators of this new handheld? They could try going for another Sonic Advance-style game, but I don't know.
Think about this for a second: What if Sega is thinking about making a fully 3D Sonic game on the 3DS? Possibly a lower res (graphics wise, not technical wise) version of the Wii U title? Does that not sound pretty amazing? The 3DS can surely handle it.
If they do go for a 2D Rush-style game, I think they'll lose a lot of buyers on it, because the Handheld games have been essentially the same since Rush. People are getting bored with it.
Goodbye Hedgehogs, Hello plumbers!