Did you already see this proposal? Specify and display relations between pages/tags
The idea is that a multi-level folder structure is a tree extracted from a graph; instead of having a predefined folder structure, the user could use any property:: as an indication on how traversing the graph and so be able to browse that tree.
We could even concatenate more properties:: as indications, for example genre::, year:: and artist:: to browse music albums starting from genre folders, then years and then by artist.