The 3DS actually has a GBA CPU that was used when Nintendo gave some free GBA games away to early 3DS buyers after they lowered the price, as a sort of refund for the difference in prices. You can access it now buy jailbreaking your 3DS, but if you have a New 3DS, emulation on the main CPU is more convenient.
Similar situation with the Wii U. It was technically capable of natively running GameCube games, but Nintendo locked out the functionality. It can enabled with homebrew.
