There could be output formatting options like limit:5 and format:with-summaries to start with.
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the output could be transformed with other plugins with their own formatting language / options (for example a list of columns to show).
What are current rules for oneboxing regarding this question?
Since the result is filtered with the users individual rights could one consider caching the unfiltered result and a filtered result for anonymous users, applying permission checks on demand for users with more rights?
Current internal oneboxes have the option to be expanded.
A similar approach might update the cached version on demand (with throttle).