How is this tracked currently/for other things (wikidata?) How is this displayed (sidebar/sister projects templates?)? We need more than just sidebar/bottom page stuff; is information that needs to be called out more on coordination pages than on content pages.

Uses:

• Linking between projects themselves once made, for better collaboration
• Finding and showing existing relevant projects when making a new project so that maintainers are aware of them and can reference/link to them from the start
• Making users aware of other sister projects that may be more relevant for certain aspects of the WikiProject than the current host, so things can be added elsewhere instead of discarded
• Allowing for translation integration between different-language projects