One thing that needs further investigation is the degree to which distros adopted systemd because they'd rather not maintain patches for udev, logind, KDE, GNOM

One thing that needs further investigation is the degree to which distros adopted systemd because they'd rather not maintain patches for udev, logind, KDE, GNOME, Wayland, etc. to keep them decoupled. I have a hunch that for !RedHat, the motivation to switch comes just as much from not having to fight upstream (if not more so) than from systemd's relative merits. After all, there are plenty of different init systems, but only one of them is coupled to the rest of userspace to a significant degree. Also, I wouldn't write off Solaris zones :) They're pretty powerful--in some ways, more so than LXC is today (syscall translation comes to mind).