Developing Expanded Games for SNES?

bluefoxlucid writes: I've recently acquired an FC Twin, a console that loads both SNES and NES video games. The patents on both of these Nintendo systems have all expired, making custom hardware and games legal without a Nintendo license. Besides letting me play Super Metroid again, this has sparked an idea: since SNES hardware can be feasibly obtained, why not create an open dev kit? In my quest to decide the feasibility of this, I've looked to the expansion chip capabilities that spawned the Super FX. My thinking is to drop in a small ARM or eZ80 to load developed games from an SD card; but I don't know much about the SNES technically, so I can't even give a rough sketch on how this would work. Does anyone have any good information on the SNES hardware, or know somewhere I could look to get the info I need to do this?