It is time for the next step in Wikipedia-Wikidata: after creating an article or category being asked in a pop-up or new screen (etc) if already an article about this subject exists in another Wikipedia, if yes: way to connect it to that article, if no: let user add it to Wikidata + help to add some basic properties (instance of, if human: gender + birth/death dates (etc), if taxon: scientific name (etc), etc).
Too many times users forget to add articles to Wikidata, even while there is an existing item for it. This results on large workloads for other users in checking if subjects already exists, missing properties, etc, while a simple pop-up would help to remind the creator and makes it easier to do this.
Having articles and categories added to Wikidata is a convention, a basic guideline that applies to all articles and categories for many years (earlier as requirement to add interwikis at the bottom of the article).