When we focus on /usr, we tend to keep forgetting the trend of moving the old role of / into initramfs. The role of / has been a minimal system that contains enough tools to initialize a "multi-user" system, including a /usr partition that was not readable by the boot loader. With more complex setups reaching beyond RAID 1 on the / partition, initramfs has come to our rescue.
I don't see any signs of getting rid of / anytime soon, it just moves over to initramfs instead. And when all necessary repair tools are usable from an initramfs shell, it will all look just too familiar like the way it was in 1992.