http://blogs.sega.com/2013/12/03/sega-3d-classics-–-3d-sonic-the-hedgehog-interview-with-developer-m2/?6866309=1
Naoki Horii, president of developer M2 who has been making the SEGA 3D Classic games for the 3DS, talks at length about what they had to do to get Sonic the Hedgehog to run in 3D at the right framerate.
They made a MegaDrive emulator for 3DS called 'GigaDrive' (note: it's not mentioned but that was unofficially the early codename in 1991-92 for what eventually evolved into Project Mars (Genesis 32X) and the Saturn.
Here is the relevant part where he mentions the SuperGrafx:
With regards to the GigaDrive’s architecture, what level of hardware are we talking about?
NH: We’ve expanded the flexibility of the MegaDrive, to a larger extent than for instance how the PC Engine Super Grafx multiplied the number of sprites and backgrounds that the PC Engine had, and added memory to it. With the GigaDrive, Video Processor functions were added for the expanded game functionality, there are more sprite tables, you can use six background layers, the backgrounds have depth, all objects have depth, etc. Once you’ve got all this working, you can build Sonic The Hedgehog in 3D.
The whole interview is great but I won't mention any more since that would be going completely off topic. I just think it's kewl that Naoki Horii mentioned the PC Engine SuperGrafx and it's featured on Sega's blog