Actually, php with docker is really nice and simpler compared to the old "install Apache/nginx to your server" method. Upgrading is easy, just pull new images and restart the containers. Horizontal scaling is also a lot easier using stuff like glusterfs as volume driver. It even easier if your app is modern and don't need ability to self-modify source code as you don't need fancy volume driver.

If you decide to drop dockerized setup in the future, I imagine it should be easy to do so as all you need is move the source code to the new host, is it not?