While I personally like using the iOS app to read, I have never used the iOS app to edit, mostly because editing is just easier to do on my computer. So I wonder if moving readers to the app - which has benefits for the reading experience - will lower awareness that they can edit? This concern might be complete speculation however.
Perhaps this addition could be tested with a smaller group of viewers, to see how many wikimedia.org viewers will actually scroll all the way down and even see the icon. That way the positive or negative effects could be tested.