There are already freakingly lot of pages in "Data" namespace in Wikimedia Commons ( https://commons.wikimedia.org/w/index.php?title=Special:AllPages&from=&namespace=486 ), but there is no categorization and it is impossible to find anything there. Unlike other namespaces, if you put "[[Category:Something]]" at the end of a page in "Data" namespace, the page will not be added to a category, but a syntax error will appear. Adding a possibility to categorize "Data" namespace is absolutely necessary and should be done somehow.