Comment # 10 on bug 1048338 from Olaf Hering

(In reply to Jiri Srain from comment #9)
> I don't think that we have ever supported sharing a root filesystem across
> multiple systems, it may have worked just by coincidence. We do not do that
> even for uEFI partition, which - to some extent - is designed to allow that.

This is not about multiple systems on a single filesystem. This can not be
easily done without chroot, even then it may not work...
The difference with btrfs is that it allows many entry points into the
filesystem (subvol=), while others have just a single entry point.