Comment by deaddodo

The biggest limit with these older consoles is the VDP/PPU. You can't just render directly to the screen because a framebuffer doesn't exist, instead you have to render to tile and then have the pixel pipeline render those sequentially to screen. So you're fundamentally limited by how fast that can update.

Systems with DMA like the Genesis could just act as a dumb framebuffer to whatever the cartridge decides to dump down the address lines. The Gameboy is a little more difficult, but could also theoretically do it as well if you decide to dump the FPS a bit and/or lower the resolution, and buffer the frames. Which is essentially what the faceball2000 devs had to deal with. And you can speed that up a bit by "racing the beam" (rendering the next frame to a previous tile as the next tile is blitting).