I'm working on a website whose purpose is to bring the community a series of collections of files on a given subject: a neighborhood of Buenos Aires.
The collections consist of audio files, images and texts from old diaries, family albums, albums of institutions, etc..
I must say that the site grows as we get new files.
With all these files and the information we are creating a database. Since these are files that are not our own but we obtained, we try to make as many meaningful relationships as possible, so you can access documents in different ways.
The problem arises when trying to classify the classification. When a sub-category may belong to more than one senior.
For such categorizations I think wikis have the best system because the data are linked in a network rather than a hierarchical system.
That's the main reason that whenever I submit information to the site, I think about moving to a wiki.
So I think a future version of WordPress should implement a system of categorization as a network rather than hierarchical.