We should be able to find the playcounts of all media within a given category, not just individual files.

The API supports this, but it can go very slow (understandably) depending on the size of the category. Instead we might do this client-side, and show a progress bar just like we do for Massviews. Either way, we face a difficult UI and coding challenge, because we're basically mixing two types of views -- the more basic "chart" view you see with the current Mediaviews (and main Pageviews application), and the "list"-based apps like Langvews and Massviews. It won't be easy, but it can be done, hopefully within the next month or two.