I am looking forward to have such a document provider extension as a wrapper to all supported cloud services within Boxcryptor. That would btw also allow cloud services to be used in other apps even though they might not have an document provider extension right now. I hope there are no restrictions from Apple that would not allow such a kind of extension.
This is basically what we have already on OSX by having a logic device that allows the access to all encrypted services using the normal file operations.
So far, opening of encrypted is kind of possible by creating a copy from inside the Boxcryptor app, but storing from an app like PowerPoint into Boxcryptor is not possible at all, which finally leads to storing the file unencrypted in the actual source cloud service.
For me this is one of the most important features on iOS and it goes hand in hand with support of the latest iOS multitasking features supporting iPad Pro. I hope you guys prioritize these accordingly ...