I think Stephen Hackett is onto something with regard to inter-app file management in iOS. As Android has shown, it’s a really hard user interface problem to solve; they’ve taken a good crack at it, but it’s still not great for users.
I’ve been thinking about file management in the future for a while now. One of the things I think might change is a shift from a file/folder metaphor to a project-based metaphor. Files from one project, regardless of their location in the system, could be grouped together, and the same file could be shared between multiple projects. That’s kind of what tags in Mavericks does, but I imagine a much more intensive implementation.