Goal of this issue is to implement new core metric computed for every plugin using LogAggregator class to pull out report data. Metric can be number of unique config_id's across given timespan (similarily to unique visitors).
Business case for this metric is when instance isn't using cookies for some reasons, and unique_visits metric is simply useless.
It could be set in config file to process it or not to save some not needed computation.
It would also be very nice to have ability of making it default displayed metric across reports (for ex. instead of nb_unique_visitors).
Please let me know if you have any questions about it and when possibly it could be implemented?