Although I like using my iPad, the invisible is one major drawback. Thanks to Rene Ritchie I know that I am not alone at last.
The average user doesn't know about filesystem details and perhaps doesn't want to know but if you try to use a device like an iPad in a productive or even professional manner, you will come to the point where a filesystem is needed.
On a PC or Mac it is not uncommon to work on one file (or call it chunk of data if you don't care that it is actually a file) with more than one application, maybe because each has that single feature that is needed to make progress. Yes, apps can exchange files on iOS but it's crippled and there is no way to be sure that one app can give one received file back. The cloud could be the solution for this but every App developer has to reinvent the wheel if he/she wants to support iCloud and/or Dropbox and/or ...
One place outside the App sandbox where every app can read/write would be fine and just like iOS prevents the starting of unknown (AKA unsigned) apps it could ensure that nothing can be ever executed from this filesystem.
Would this be the Überfilesystem? ;-)