Follow-on from. During use a module may create non-default configuration files; that is, files that are added to the live configuration directory, but are not provided as defaults within the module's config directory. For example, one may use image.module to create custom image styles with the GUI. Files will then be created for each image style, and will not currently be automatically removed when uninstalling the module.
There is a policy/meta issue here, namely, should it be the responsibility of core to clean up these files, or should individual modules be expected to implement hook_uninstall and clean up any non-default config files? If the former is true, we need to determine how to associate config files with their module so that they may be safely removed. The easiest method for doing this is probably to make a policy that all modules must namespace their config files by prefixing them with the name of the module.