Distributed storage is still a big issue for sure. There are some options, but none are ideal. One option is to map to host and use NFS to share across hosts. Another option is to use something like Convoy or Flocker, which come with their own complexities and limitations. Hopefully more progress is made on this front.

As for the wordpress app and other issues mentioned, it's actually very simple:

    nginx:
        build: ./nginx/
        ports:
            - "80:80"
        volumes_from: 
            - php-fpm
        links:
            - php-fpm
    php-fpm:
        build: ./php-fpm/
        volumes: 
            - ${WORDPRESS_DIR}:/var/www/wordpress
        links:
            - db
    db:
        image: mysql
        environment:
            MYSQL_DATABASE: wordpress
            MYSQL_ALLOW_EMPTY_PASSWORD: "yes"
        volumes:
        - /data/mydb:/var/lib/mysql

This isn't a "production" config, but that wouldn't look that much different. The real beauty is that I found this compose file with a simple search and very easily made minor tweaks (e.g. not publicly exposing the mysql ports).

You might run into permissions issues if you use host mounted volumes, but I have not. Normally I prefer to use named volumes (docker-compose v2) and regularly backup the volumes up to S3 using Convoy or a simple sidecar container with a mysqldump script.