I think this whole / -> /usr or /usr -> / discussion highlights the need to re-think the FHS more drastically. Clearly not everyone (like me, for example) is happy with moving / into /usr and I keep seeing complaints about use cases that break when you do this. I also see despair from some people who say that we're fooling ourselves if we pretend that there aren't programs that presume /usr is always there when they shouldn't.
Maybe it's time to lay out a new FHS, beginning by describing all of the uses we need to get out of it, and make one big painful move instead of this piecemeal nobody-is-happy stuff.
Q: If initramfs is the new "minimal root" and we have to maintain it anyway just to boot, can we maintain it in its own partition mounted on /init/ and re-do the boot process to use that path at all times whether it's a real disk or a ramfs?
Q: If /tmp and and /etc are local-only, but /usr is not, is there a way we can signal that in the FHS so that people can't be easily confused in the future?
I don't know, but it seems like fighting about what should go in /usr and whether anybody really needs to share it over NFS is idiotic and tangential to the real issue, which is how to solve problems people actually have. Nobody seriously cares where files are located as long as everyone can still do what they need to do.
It's a bit like Debian's multi-arch. There are a lot of ways to solve a lot of little problems but only a few that solve them in a big way for a long time.