David Siller is the creator of Aero the Acrobat, and worked with Sunsoft's U.S. office for many years, before going on to work on Maximo and other titles with Capcom. He's been showing some of his old unreleased designs via his facebook page - really, he should have these all on an accessible website somewhere, but for now, I'll just highlight one odd thing he was pitching to Japanese peripheral maker Cyber Gadget (which I believe is this company, still going strong). I'll use his description:
"This is a "HACKER" device that was intended to allow Famicom/NES games to be hacked by changing the main player sprite shape, color assignments and animations. Also, the same for many of the NPC's! The software is downloaded into a PC and altered using appropriate editing tools and then uploaded into a blank Flash cartridge shaped like a Famicom or NES version."
It never saw the light of day, perhaps for obvious reasons. Nintendo was quite particular about what it wanted on the system, I can't imagine they'd want users to be able to screw around with all the code. More from Siller again in the near future!