That's what makes it approachable (though I don't agree it has an semblance to go other than "FROM <ref>" being fully qualified (minus the carve-out for Hub), b

That's what makes it approachable (though I don't agree it has an semblance to go other than "FROM <ref>" being fully qualified (minus the carve-out for Hub), but even then it can absolutely act more like a local import if you have an image with that ref locally (or you can even override it in your build command in a couple of different ways). Also note, Docker can build whatever format you want, it just defaults to the Dockerfile format, but you can give it whatever syntax parser you want.