People have been clamoring for such for as long as the iPad and iPhone has been users hands. The issue is that apple seems to believe we don't need an exposed file system, just look at the latest iterations of Lion and Mountain Lion.
It is part of the post pc company philosophy in so far that traditional features of an OS, like a file system (exposed so a user can save to a specific folder) is no longer needed. They've shown that iPhone and iPads can live within that concept and I think OSX is heading that way albeit slowly.
iCloud's document sharing is kind of a file system for iOS. I don't think the file system is going anywhere with OS X, even if Apple continue to dumb it down.