[mzzter]

Last time i researched adding shift registers was over a year ago and I didn’t find many examples (I vaguely recall one possibly with qmk), and very little public discussion besides a reddit question. Popular guides like ai03’s at the time recommended upgrading to a microcontroller with more gpio before introducing shift registers.

Searching again, looks like zmk added support for the common 595 shift register: https://github.com/zmkfirmware/zmk/pull/1325

Edit: You could avoid using diodes, but diodes increase the number of switches possible via a matrix more than shift registers do by giving you more gpio. I’d imagine one can use both together.