Moving every thing to /usr to make the filesystem more sane.
Meaning that the system no longer supports /usr in a separate filesystem: http://freedesktop.org/wiki/Software/systemd/separate-usr-is-broken.
Of course, you can still use /usr in a separate filesystem from / if you boot with an initrd, but you now almost need half an operating system (busybox, rescue shell and utilities, perhaps support for lvm and/or RAID) just to boot your real operating system.
Why would you want /usr on a separate filesytem? Perhaps you want it in LVM, so you can resize it easily if necessary (maybe to make room for installing a new desktop environment, for example), but don't want you root file system in LVM. Perhaps you want to periodically fsck /usr on boot, and fall into single-user mode if it fails. Perhaps you want /usr (which is a read-mainly file system) on a small SSD, and all other file systems (which are written to more frequently) on spinning disk storage. Perhaps you want to mount /usr over NFS. Not that I can still see many people doing this but it seems a pity to prevent something that has worked fine in the past - and in these days of "running applications in the cloud" it seems Linux will no longer run applications in the local network (ie. NFS-mounted /usr).
Seriously, read the level of professionalism and maturity on that page. This is the level or maturity to which Linux slowly seems to be sinking. As a long-time Linux user and supporter I find this deeply disappointing.
And what's the reason for all this? Because the udev developers can't wipe their own a{r|s}es, put their house in order, and properly sort out which files go where (or at least sort out what needs to be done to mount any necessary non-root filesystems, mount them, and then continue with any programs/scripts which use them). Instead, all of that gets pushed out to initrd (ie. oh no it's hard, let's give it to someone else to do). Seriously, they're like a bunch of 8-year-olds bragging to their friends that they won't clean their bedrooms, even when mummy thinks they should.