Yes, this is convenient and speeds up Dockerfile development. At the same time, this is an issue when you consider using Docker as a part of your production deployment toolchain. I think both ways should be supported: incremental multi-layered images for development or exploration, and then possibility of creating a single, compact image for lower overhead in deployment. In a perfect world, it would be a switch for `docker build`, but I'm not fluent enough in Go to propose a solution on that side.

Some people have considered another approach: flattening an existing stack of images. Scripts for that are linked from the Docker issue on GitHub. I wasn't able to get any of these working, and the logic behind these seemed quite convoluted.

Still, my script is just a proof of concept - I tried whether it is possible to take the approach I use internally for Docker build scripts, and use it to build Dockerfiles. It seems it's possible, and it delivers good results. Time and actual usage will show whether it's a good idea; if this approach makes sense, it will hopefully make its way to the Docker core, and my hack won't stay relevant for too long.