Dropbox's success depends on OS' file system representation. It's currently the perfect solution for the folder/file system but new systems like iOS and Android don't need a dropbox. I remember reading that Steve Jobs wanted to abstract out the folder/file representation for a simpler and easier to use iOS. They hide the files inside each app and it is all synchronized by iCloud. Dropbox clearly is aware of this paradigm shift and that's why they are pushing their new SDK and have a conference to promote Dropbox integration with any other apps.