I have XUbuntu and Arch on a laptop, I'm sharing /boot partition between these distros mounting it on /mnt/boot and bind-mounting /mnt/boot/xubuntu or /mnt/boot/arch onto /boot; it works fine even when updating initramfs, no manual intervention never.
I would like to do the same for /, for example, having /xubuntu and /arch directories on the root partition and selecting one of them on each initrd. I know it is not the same case as for /boot, because initrd must first mount that filesystem on /test, for example, and later a pivot_root must be issued to make /test/xubuntu or /test/arch the new /.
It is possible to share / between two distros in the way described above?