The problem with that design is that in a lot of use cases, images don't necessarily need to be 'referenced'. For example, I'm using docker for a build/test system; we spin up a container from an image, run some stuff in it for a few seconds, and then shut it down. 90% of the time, the images are 'unreferenced'.

The other suggestion, put forward by a docker dev in another comment, is to have a clean command for unnamed/untagged images. Our build system has 'buildbot' (python package compilation) and 'software' (test environment) images, so this sort of automated cleaning would get rid of all of that extra crap that we have lying around.

The big issue for me is stacks of changes. Like git, anything you commit, remove something from, then commit again still takes up that space forever until you consolidate down. Which you can't do automatically.