Concept for an extended sandbox + centralised document viewer for iOS

I'm not sure if this has already been suggested, but come to think of it, why does every single app need to have it's own sandbox in iOS (and in Mac Appstore apps) ? Apple loves to say that it's 'simplified' the way we interact with apps by killing the file system. In reality the simplicity is only cosmetic. The way we now interact with files on iOS is a royal mess.

If i'm working with pictures, I want all my photo apps to have a common pool of storage. Letting me edit metadata, edit the photos themselves, share and sync my photos as I please, using any and all of the photo apps I have. I don't want to have to import/export from camera roll every damn time.

Same goes for PDF files: Every time I open a PDF in an app, iOS copies the PDF into the App storage EVERY time. I needed to fill in, mail and then store a 90MB PDF file. I ended up with 3 copies of the same document across 3 different apps.

I think it would be much better if apps had their local storage pooled together on the basis of the "type" of document. By "type" I don't simply mean file extension. PDFs in one pool, Presentations (ppt, keynote etc) in another, same with Documents (word, pages, txt, md..) and Spreadsheets. This helps in doing away with file extensions, so basic users don't get confused. At the same time, it lets power users juggle their data across apps as they please. Photo apps and Music apps would benefit the most with this expansion of the sandbox. Apps like Audiobus allow you to bring your audio apps together in ways that simply would not be possible otherwise, which is awesome yet a a bit of a shame at the same time. A mature platform like iOS should allow all that by default.

The "All my files" view in finder in my opinion is fantastic. I never really need to hunt around for my documents on my mac anymore. I don't have to care whether the file I want is on my desktop, or hidden in some obscure folder somewhere, it's all there for me to see. iCloud integration is horrible in iWork apps themselves. It's a trippy and convoluted solution to keeping files in sync. I don't understand the need for a separate "iCloud document viewer" in the OSX iWork apps, when surprise surprise- the "All my files" view in Finder shows both Locally stored documents and iCloud documents?

Apple somehow managed to make the whole concept of the file structure totally redundant and much more intuitive on the Mac by this one simple feature, either completely by mistake or by a stroke of genius.

Why does that simplicity not exist in iOS?