To allow for VCS-friendly customization of dependency resolution process, a feature that allows for files referenced in an <include> directive of an ivysettings.xml file to be missing without it triggering an error.
With such a feature, it would be possible to write a global ivysettings.xml file that references a default setup of resolvers/repositories for a project, commit it into a VCS and then never edit it. Instead, an "optional include" directive will point to a file with standardized name, say, ivysettings-local.xml. The file may be missing (which results in the project-default configuration being used), or a developer can create such a file and define an alternative resolution configuration for his own use. The VCS can be configured to ignore the ivysettings-local.xml file, thus absolving the developer of the need to ensure manually at each check-in that the file is not committed into the VCS.
Currently, a similar feature is implemented for properties files. Unfortunately, it is impossible to, for example, override a project-default resolver with a user-specific one only via use of properties.