I made a quick demo of browsing Wikipedia categories by popularity.
The video is here (sorry about the audio quality):
http://www.youtube.com/watch?v=f3QXwY-XR28The source code is here:
http://en.wikipedia.org/wiki/User:Wakebrdkid/Popular_category_browsing
If other people like having an option to sort categories that way then article traffic
might be a good property to store on Wikidata.