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.
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.
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.