Okay, but they're Apple. They could add jails. They could even hack it in by dropping in FreeBSD code, again. (Yes, XNU isn't really BSD, but they're kind of BSD when facing towards userspace so it should work.)
Man it would be so awesome if MacOS had jails. I’m off Mac, and that wouldn’t get me back on it, but it would be amazing.
They could. Then what software would run on it. What sort of tech talent would operate it.
If it only made Darwin jails, then it could still run any native software, and would likely end up running a lot of homebrew/macports. (This started by discussing Apple internal servers, so just running their own stuff plus nginx et al. would be fine.) Or, they could take another cue from FreeBSD and illumos and add a Linux personality, or do like illumos and NT and bake in a VM that was seamlessly integrated and use an actual Linux kernel to run stuff.