A NES SoC would fit easily within the area of a microSD card containing all ROMs ever published for it, and the embedded controller in the latter would still have a few orders of magnitude more transistors and be faster than it.
You would likely get into “full compatibility” lawyering very quickly. Many of the consoles have weirdo hardware components in some module or another that is still poorly understood.
And it still has the original controller/memory card ports!