Sad that a keyboard even needs to say that it's "privacy-conscious." What a world we've built, where one might reasonably worry that their keyboard _isn't_ private.
- recording your keystrokes in non-volatile memory, to be extracted later?
- exfiltrating them in real-time via Bluetooth (yay for wireless peripherals), WiFi, LoRa?
- asking the OS to install a driver, which (even if approved/signed) could have exploitable security holes?
The main hurdles are scale and sophistication, which, with an all-software "keyboard", were no longer an issue.
And PS/2 had a maximum draw of 100mA so even piggybacking on that would be challenging I'd assume(?) - not an expert. A Teensy which was benchmark for lots of custom keyboards can pull most of that [1].
[1] https://forum.pjrc.com/index.php?threads/teensy-3-6-vs-4-0-m...