Coul you support MacOS
It's a great application. Could you support MacOS in the future?
The interfaces it's using and all of the evdev/X11/Wayland jazz is very much Linux-specific. I'm not even sure BSD support could be easy. macOS is an utterly, completely different thing and by the way, Karabiner exists there and I've heard a lot of good things about it.
I don't know if this is something I am allowed to say because this is unofficial information (rvaiya, sorry if I am annoying you), but I have heard that rvaiya is working on a Windows and macOS version of keyd and that the basic operation is already done. Maybe if you ask, they will let you beta test it.
Sadly I haven't had much time to work on this. I do have some toy prototypes lying around, but nothing suitable for publication. I have some fairly extensive design changes planned for the next version after which I would like to invest some time in multi platform support, but that is still some time off.