The real new hat is search and all major OSes are doing this more or less correctly now. I don't recall the last time I browsed to a document.
Also worth mentioning that the concept of "documents" is itself a quickly aging hat. With some very few exceptions most documents are tied pretty closely to just one app and apps and those apps in turn can have more specific ways of handling those documents (i.e. projects, libraries etc).
The internal representation of files and programatic access is another matter - we do need a better way to segregate access and assign metadata to files. Possibly a relational file system would be the way to go, but it's not a problem that very urgently needs solving for anyone so nothing too exciting there for a while....