I started a machine control project a while back and tried out this project for some of the lighter IO stuff
Basically that project uses an Arduino to read/write IO and communicates back with a PC running LinuxCNC over serial. It just consists of an Arduino sketch and a Python file that resides on the host PC.
I've used this and had it working but I wasn't thrilled about a few things in that project and I eventually got busy and shelved it for a while.
One of the things I wasn't thrilled about was the matrix keypad setup. There were bugs in the code that I got a friend to fix and submitted. Ultimately I still was not happy with the way scanning the keys and writing the LEDs with a pulsing effect worked.
I would up redesigning a keypad that used 4 I2C IO expanders, but that's pretty much where I stopped. fast forward to now and I want to get back to work on the thing this was intended for but since the I2C IO abillity was never added I won't have the working keypad.
I did manage to scrape up an ugly arduino sketch to test the keypad and it fully works by itself so I know the I2C setup and all of that. So what needs to be done is basically that git project would need a new type of IO assigned that runs back to the I2C in the same way it uses regular ins/outs and adds this to the serial protocol to communicate with the Python side. I don't think it really needs any testing on the programmers side as long as it just follows the same methods as what's already there. The fact that this is for a "keypad" doesn't have any bearing, it's just inputs and outputs to MCP23017 IO expanders.
This could be a paid gig if it's reasonable or I'm pretty decent with PCB design if anyone wants to barter. I did submit a git issue to see if the original creator wanted to add this but I suspect he is too busy or not interested. This would either be merged into that project or into a public fork.