Forget the entire NES in a cartridge thing. Forget I even mentioned it. A modder on the BenHeck.com forums known as “G-force” has managed to get a famiclone aka Super Joy III, into an NES controller.
The famiclone already had 70 built-in pirated games, but that wasn’t gonna cut it. So he added a cartridge slot on the bottom so he can play any NES game he wants. The Nintendo logo is even backlit. Pretty damn awesome. As for the rest of you, allow me to paraphrase a classic AC/DC song. For those about to mod, we salute you.