That's an interesting idea. I don't think you can create a subcommand/plugin for compose but creating a 'docker composepussh' command that parses the compose file and runs 'docker pussh' should be possible.
My plan is to integrate Unregistry in Uncloud as the next step to make the build/deploy flow super simple and smooth. Check out Uncloud (link in the original post), it uses Compose as well.