okay, then I'll bend the rules of GBJam harder than anyone ever has, just wait for my entry!
Well VR wouldn't really push any rule since you'd just be looking at the same game through your visor. You could take any entry really and throw VR at it, although it could be cool with a 3D game like I'm doing. I'm too cheap to have any vr accessory anyway :)
Anyway, I was talking more about pushing the 4 colors limitation to its limit. Since it's 4 colors at any given time and not 4 colors max for the whole game, you can expect copious amounts of palette swapping. Like literally swapping the palette every frame to crossfade between different palettes, change brightness, fade in/fade out, oscillating, taking certain colors and flickering them with another color every other frame so the brain fills in the gap and creates the illusion of more than 4 colors, etc. A bunch of crazy stuff like that. I've already got some of that implemented too and it's awesome.
It's almost poetic really, developers back in the day tried to push the limitations imposed by their hardware, and now we're pushing artificial limitations imposed for fun.