“But fundamentally, there is a mismatch between the narrowness of hierarchies and the rich structure of human knowledge, and the proposed system will not presuppose the features of HFSes.”
Folders copy a filing cabinet, where each sheet of paper lives in exactly one drawer. A photo of your kid at the beach belongs in three folders at once. Git and image boards already solved this with hashes and tags. Desktop operating systems still ship the 1970s model.