[geofft]

> which means you’d be able to run another instance of macOS in a container

This is not true, for multiple reasons. Strictly speaking it only means you'd be able to run another instance of Darwin in a container. And, as you surely know because your tone of voice implies you bear immense knowledge, a Docker-style container is not a full OS: it doesn't run an init or normal system daemons, so it wouldn't even be a full instance of Darwin, so it wouldn't have to support functionality only needed by launchd or system daemons (e.g. WindowServer). It would just need to let you run a stanalone program in a chroot + separate network, PID, and IPC namespace + apply resource controls.

Furthermore, since most people are using Docker for developing software that's going to run on Linux, there would be no real need to virtualize the parts of XNU that aren't also provided on Linux - notably all the Mach stuff. You'd just need to provide a BSD-style syscall API to programs in a container.

[jsjohnst]

> it doesn't run an init or normal system daemons

There’s no technical limitation stopping you from running init or system daemons inside a container, it’s just an anti-pattern and missing the point of a container in most cases.