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Conflict Resolution
Currently, there is only one implementation of conflict resolution in Maven. In certain cases, users may wish to use alternative methods to resolve these conflicts, maybe even opting to fail the build when a conflict is detected.
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Specification Dependencies and Provides Notation
It's possible for a given API to have multiple implementations. For example, the JavaMail API has the reference implementation provided by Sun, along with multiple open source versions. In many cases, POM authors will want to specify that a project depends on JavaMail, but won't necessarily want to dictate which implementation of the API is used. Moving to specification dependencies will solve this problem. The specification POM will serve as a pointer for a set of libraries which implement the API. The specification dependency would then be resolved in a number of ways, possibly with user preferences factored in via settings.xml.
Provides notation would be related to specification dependencies, but on the opposite side of the artifact relationship. For instance, Sun's JavaMail implementation would specify that it provides an implementation of the JavaMail API, as would the javamail library built by Geronimo. It would act as a reverse mapping of which API(s) are provided by a given artifact. This provides specification might need to be plural, to allow a single artifact to implement multiple APIs, thereby satisfying multiple specification dependencies from a single build.