The Mario Kart example is interesting, because you can achieve it's effect by simply teeing off the GPU output both to RAM (scaled down to native) and directly scanned out.

The neat thing about the perfect dark effect is that they read modify write the entire framebuffer and it represents the full scanned out frame, so in those cases you'd need to drop scan out resolution back down dynamically, where as on the Mario Kart example you can keep the higher scan out resolution.