You'd be disappointed about many retro game jam rules...
At least the Game Boy is very predictable: the biggest limitation is the screen and buttons so if it's graphics based on 8x8 tiles plus reasonably sized sprites, or fullscreen pics at low frame rate, it can most likely do it.
However, the SNES could do wild stuff (some graphics modes feature high color depth or double resolution) but anything more complex than All Stars required quite a bit of trickery. Yes, 512px horizontally, 480i, 3D perspective of a plane, color math etc. have been achieved but each takes a significant portion of the resources so it's very hard to pin down the limitations of what would be possible at once. Not to mention enhancement chips...