I stumbled upon setting up keepassxc on windows side to enable ssh agent support with npiperelay and socat. The documentation of a recent fork mentions that even if the npiperelay exe is installed on wsl side, it will work.
windows.npiperelay is actually packaged in nixos, however I get the error that nixos won’t let me build this on linux.
I am not sure whether enabling is enough for this to actually work, maybe the exe really needs to be build for windows and can just reside whereever we want.
Nevertheless, this is an awesome little thing. It would be so cool if windows exe could be managed via nixos-wsl.