In Void Linux, /bin is a symlink to /usr/bin. While it may seems as an iconoclast move, as we all know that /bin should only contain the utilities needed in single user mode, further reading on the matter may convince you otherwise. This issue is unrelated to systemd and other distros might follow suit in the future.
https://www.freedesktop.org/wiki/Software/systemd/TheCaseForTheUsrMerge/
http://lists.busybox.net/pipermail/busybox/2010-December/074114.html
When the operating system grew too big to fit on the first RK05 disk pack (their root filesystem) they let it leak into the second one, which is where all the user home directories lived (which is why the mount was called /usr). They replicated all the OS directories under there (/bin, /sbin, /lib, /tmp...) and wrote files to those new directories because their original disk was out of space. When they got a third disk, they mounted it on /home and relocated all the user directories to there so the OS could consume all the space on both disks and grow to THREE WHOLE MEGABYTES
Of course once the split existed, some people made other rules to justify it. Root was for the OS stuff you got from upstream and /usr was for your site-local files. Then / was for the stuff you got from AT&T and /usr was for the stuff that your distro like IBM AIX or Dec Ultrix or SGI Irix added to it, and /usr/local was for your specific installation's files. Then somebody decided /usr/local wasn't a good place to install new packages, so let's add /opt! I'm still waiting for /opt/local to show up...