Hi,
I just published the 2020 report on Wikidata Property constraints, the results of an analysis carried out thanks to a Rapid grant from the Wikimedia Foundation.
https://www.wikidata.org/wiki/Wikidata:2020_report_on_Property_constraints
You can take a look at the report and complement it with your comments and suggestions to improve the system of Property constraints on the talk page.
https://www.wikidata.org/wiki/Wikidata_talk:2020_report_on_Property_constrai...
Although the scope is limited, I hope you find the content useful.
Thanks to the Wikimedia Foundation, to Wikimedia Deutschland, to the 58 active editors who completed the survey I sent them in December and to all those who dedicate their time and effort to improving the quality of Wikidata data.
Regards, David