In T95287 we'll get a new identifier datatype for properties. In the page_props table we track several attributes of a page like the number of claims (wb-claims) and the number of sitelinks (wb-sitelinks). Would be nice to track the number of identifier properties on an item like the number of sitelinks. How to count exactly I'm not sure. One option is to count the number of P identifiers, other option is to count the total of number of claims. If for some reason the same identifier property is used multiple times on an item, the results will differ. I would probably go for the second option (number of claims), because that's closer to how wb-claims counts.
This page_prop could be used in a similar way as wb-sitelinks: To rank items and to suggest items to work on.