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Internationalization (i18n) would be a nice to have. One language could be globally configured. Supporting multiple language would be better, but it's not a top priority. It could be detected from the browser (which is nice, but a default value would also work) but it has to be user-changeable using a drop-box or link of some kind since browser language might not be what the user prefers to see.
Display group relationships
Visual display of groups impacting membership of a given group. Would illustrate subgroups and composite factors, perhaps expanded by levels.