The case for the /usr merge

The point is that the initrd is the appropriate place to put those tools as it can be reliably loaded using he same method as he kernel. You could have a root filesystem that requires a module or network mount so you already need to support this kind of complexity in the initrd. If you don't want an initrd for some reason then this naturally limits the filesystem setup you can boot off of.

The problem with maintaining a split system is that it is currently broken on the major systems and has been for some time. At least a dozen binaries in the base system depend on resources in /usr. Fixing it by moving more of the system into the root directories seems more complex and prone to breakage than relying on the toolkit in initrd. Since all the tools you need are already in the initrd, maintining the /sbin /usr/sbin split doesn't have a point. Getting rid of the split makes the system simpler and more flexible so it seems like the right choice