Similar to this, among custom keyboard builders it's quite popular to have USB handled connected via TRRS headphone jacks between split keyboard halves [0] [1] and sometimes even the keyboard -> PC Connection being a custom TRRS -> USB cable or other exotic variations. [2]
[0] https://keeb.io/products/trrs-cable
[1] https://docs.splitkb.com/hc/en-us/articles/360010443660-Kyri...
[2] https://www.kingcables.org/products/custom-straight-usb-cabl...