But how would you go with restoring such an image? It won't be instant, there will still be a window where the service manager is continuing its work but the image hasn't been restored yet. One way or the other, you need a synchronization mechanism, so how would you design such a mechanism without support from the daemon?

You don't need a complicated case to have a race with acquiring some resource. A server opening a socket is providing a resource; clients connecting to that socket are using it. Clients should not be started before the server is listening to the socket. How would you solve this case - are you advocating socket activation by the service manager? ;)