To me, the most important feature of OS X Yosemite is iCloud Drive. For years I asked for the old iDisk to come back in a modern form. I’m happy to get it back. 

There’s a drawback to iCloud Drive in iOS, as correctly Macstories points out:

The most obvious difference about iCloud Drive on iOS is that because there is no Finder equivalent, there is no in-built app to view all your iCloud Drive files and folders like you can on OS X Yosemite. To resolve this problem, apps on iOS can implement the iCloud Drive Document Picker which will provide a popup window that gives you access to the full iCloud Drive. One such example of an app that implements the iCloud Drive Document Picker is Readdle’s PDF Expert.

and

iCloud Drive sits awkwardly as a solution to a problem that Apple created. Apple at first tried to avoid implementing a file system on iOS but have now realised that some users need it and have created iCloud Drive in a way that tries to hide what is ostensibly a file system, ultimately making it more complicated. The problem is that files still get stuck in these weird app folders, which frankly makes no sense to me. If I have multiple text editors or spreadsheet apps, how am I supposed to know which app I created the file in?

The problem ultimately is with iOS. From the beginning this operating system has been designed to hide the complexity of a filesystem. The result is the current hybrid-not-ideal situation. 

For too long I was a proponent of a filesystem-less OS, but I have to admit that it was a mistake. When Steve Jobs said that explaining a filesystem to a user was one of the most complex things to do, he was probably right. What he probably didn’t consider is that most people these days feel comfortable with the concept of folders and sub-folders. 

I think it’s too late for Apple to do a 180 on this topic, but I hope File Picker is the first step in giving users more flexibility.