The 3DS CPU would also support GBA cartridges, if there were any place on the console to plug them in. It's kind of amusing, actually — Nintendo didn't intenti

The 3DS CPU would also support GBA cartridges, if there were any place on the console to plug them in. It's kind of amusing, actually — Nintendo didn't intentionally support GBA in the 3DS. But they supported DS in the 3DS the same way that the DS supported GBA: by embedding the previous generation's CPU, as is, within the die of the new CPU. Which means that inside the 3DS's CPU is a DS CPU; and inside the DS CPU mask they reused for this, there is a GBA CPU. Which is fully functional. You tell the 3DS CPU to reboot into DS mode; then tell the DS CPU you're now talking to to reboot into GBA mode; and there you go, you're now talking to a GBA CPU. Nintendo eventually did realize what they had done, and released a few special limited-run GBA "Virtual Console" games. (But those games aren't emulated; they run natively!) You can use Nintendo's own GBA firmware to run your own GBA ROM images natively on a 3DS, if you like—though I don't think Nintendo's GBA firmware supports things like a Real-Time Clock, so you're better off using a GBA emulator there. But the potential is clearly there for someone with skills like the OP here to lift the CPU out of the 3DS onto its own PCB with a GBA card-edge socket, and then write a GBA firmware for said CPU that actually interacts with it.