Not a mature idea but definitely something we all have to figure out : how (if we should) to integrate the different "groupification" methods on Wikimedia:
* (unformal) classes item on Wikidata
* categories on wikipedias, common cats
* list articles
* ... (?)

This raised a number on issued that never could really be socially properly solved on Wikidata and Wikipedias, the overall picture remains unclear.

On the other hand there is relationship between all those objects, some categories maps to classes and to lists, some categories maps to a property/value pair, some lists articles maps to categories. There is tools to define queries from lists article, Reasonator is an exampe. Maybe we need a comprehensive review and search for a consistent model and/or a plan that could be discussed with community to gain a consensus that would led to involvement an action from the different communities  ?