I didn't see this coming. This is great news for iPad/iPhone users!
Native cloud storage integration in the iOS apps
Starting today, third-party cloud storage providers can natively integrate into the “Locations” picker in the iOS Office apps. This will enable users to open, edit and save documents from these providers right from within Office. While we’re announcing availability of the iPad and iPhone integration today, we’re hard at work on the same type of integration for the Office universal apps for Windows 10 and the Office for Android apps. So in the future, no matter what device, platform, or storage provider you’re using, your Office documents will only be a tap away.