What sort of ideas do you have about 'offline' content?
At the moment, lessons can be downloaded, and when you're left without an internet connection, 'Downloaded Only' can be selected from the side menu to show only content that is available offline. Granted, this switch to 'Offline mode' should happen automatically when the app detects the loss of data - better network connectivity awareness is something which is being worked on - but you should be able to use the app offline if you've downloaded lessons.
Is this what you were referring to? Or maybe you had something else in mind?