Feel free to add whatever occurs to you by finishing the sentence 'VFS needs ...'
vfs composition: the ability to stack vfs on top of one another, ala Plan 9. It's got it, Cache VFS - complete with write-back.
A component of this is 'vfs::add, which gives the ability to compose file systems functionally. -- 20040612 CMcC
versioning vfs: write to a file, and the diffs are store and accessed by globbing the file as if it were a directory. People have got to realise that the distinction between file and directory is a purely arbitrary and not particularly useful constraint.
Implementation ideas: use CVS or metakit as a backing store? I'm tempted to use metakit with progressive diffs. I guess it ought really to be backend agnostic, but I'm not sure I want to go to the trouble. -- 20040612 CMcC
SEH Try a versioning virtual filesystem.