There are quite a few issues with running a systemd-based distro in a container. The first being that /sys and /proc are basically not namespaced. So if you're not careful, systemd might start modifying your host. There's some work to improve this (the cgroup namespace -- yes, that's a thing now) but the point remains that allowing a root process to start touching /proc and /sys inside a container won't end well. I believe that LXD tries to get around this problem by mounting a FUSE filesystem on /proc and /sys that does a bunch of fakery. I don't like that, to be honest. It should be the kernel's job to namespace things properly.