Wrapped up my documentation on this unusual mashup! https://flatfootfox.com/typeboy-keyboard-typepak-cartridge/
I managed to fit a XIAO BLE, Sharp Memory Display, shift register, and LiPo battery inside of a Game Boy Advance cartridge. The "TypePak" is mostly just for aesthetics, but it will make swapping microcontrollers more straightforward if I use it on future builds. The keyboard itself is pretty strait-laced 58 key split ergo outside of its GBA-compatible cartridge slot. I did some experimenting swapping out volume rotary encoders for thumb switches to try and keep the Game Boy vibes going. Everything's topped off with a few FK Custom keycaps.
There's nothing quite like seeing a nicely spaced out PCB in KiCAD, only to have the real thing show up in the mail and show you just how close 0.5mm pins with a 0.5mm pitch really are. I'm really happy with how it all came together in the end though!