@whitequark the biggest latency decrease for keyboards running QMK would be to change the debounce method.
iirc the default debounce waits for N (tunable) scans of the key being in the same state before it considers the key to have changed states. and it uses some fairly high value of like 5 or 10 scans (@ 1000Hz) as the default. this adds latency for no good reason during the key-chatter period.
better imo is to make it so as soon as a scan returns the key as connected you send the down event. then you wait for it to settle, during which you wont send events for a state transition. then as soon as settling is done you'll happily instantly send a key-up event as soon as the key isn't connected for a scan-cycle
its like. marginally more complicated to implement this, and technically more susceptible to electric noise, but what the fuck ever
@artemis @whitequark qmk already supports that method, you just gotta set DEBOUNCE_TYPE to your preferred eager algorithm https://github.com/qmk/qmk_firmware/blob/master/docs/feature_debounce_type.md
@noiob @whitequark good to know, it definitely did not when i was setting it up last time