The USB thingy already exists, I actually own one for macros with dumb keyboards. Its a very small USB-device with a USB port where you can attach standard USB keyboards. It runs QMK and essentially acts as a proxy, allowing you to program macros and what-not directly in QMK. A neat, little gadget.

See https://geekhack.org/index.php?topic=69169.0

Edit: Correction: It actually runs TMK, but I flashed QMK on it.