So how about this then:

    {
      using my_socket = new NetworkSocket();
      my_socket.write("Started");
      register_callback(() => my_socket.write("Finished"));
    }

This is the case what RC solves well and tracing GC doesn't solve at all, regardless of the number of interfaces you implement. It is easy to find yourself in this situation given how much callbacks are used in modern codebases.