[NoPicklez]

I think its a good idea too, however does there come a point there you're also limited by the hardware it is plugging into? You might be able to include faster RAM in the cartridge, but will it work as intended with the original board its being plugged into.

Could you attach faster storage if the underlying hardware its plugged into isn't changing. I guess you could but I don't have a lot of experience in that area.

[KeplerBoy]

You can do pretty much anything if the cartridge is advanced enough. At that point you just output a framebuffer from the cartridge the screen should show with no computation happening on the actual gameboy CPU.

People built cartridges which stream game footage from a PC to the gameboy and relay the inputs back to the PC to "play" GTA 5 on an original gameboy. https://www.youtube.com/watch?v=pX1opw_gsBs