I really like this. At least for the nspawn case, systemd as of 242 supports loading containers from OCI images directly, but still doesn't seem to support OCI hooks or have a runc-compatible CLI, which were the other two outstanding issues identified by Poettering before it could be considered a true drop-in replacement for running container bundles loaded from OCI images.

As for just using systemd and not nspawn at all, that seems useful for a lot of cases, but not multiplexing of networked services since systemd can't assign UNIX domain hostnames and IP addresses to individual services. At least, I think it can't, can it?