I’ve just stumbled upon the GitHub - sickcodes/Docker-OSX: Run Mac in a Docker! Run near native OSX-KVM in Docker! X11 Forwarding! CI/CD for OS X! project. I think it might be worth considering for ROS buildfarm, as I remember there were always complications with OSX CI and a scarcity of resources (I assume the OSX CI was running on some real Macs?)
But I’ve not experience with OSX, so I’m just throwing this information in for others who might be interested.