Well, I don't think multiple docker daemon instances handling the same /var/lib/docker will work, the devmapper metadata updating relies on there only being a single updater, and i think thatt is the same with the container json files too, no?

But sure, we could use some other ID to base this on. However, will not two docker instances running docker inside them have the same inode for /var/lib/docker? (Assuming docker is in the base image).