Right now WikiProject article assessment metadata is all stored in WikiText in templates on article talk pages (although some of it can also be accessed via categories). This means that there are no easy ways to query this data and it has to be aggregated and reported through scripts and bots.
Then each time the template was transcluded on an article talk page, it would add an entry into a table like so:
+-------------------------------------------------------------------------+ | Page | Namespace | Project | Class | Importance | Revision | +-------------------------------------------------------------------------+ | First aid | 0 | Medicine | C | High | 73264 | +-------------------------------------------------------------------------+
It should also record a log entry each time an assessment is updated.
Once this table exists, developers (WMF or volunteer) can create tools that help WikiProjects organize their ratings.