I like to think of it it with the question: what is to reading what a text-editor is to typing?
Social features for sure. We could also experiment with crazy stuff like SYNTACTIC SPACING. Here's an illustration on a paragraph from Doug Englebart's Augmenting Human Intellect:
Reading shouldn’t be a goal —instead it ought to be cultivated as a habit .
It should be a relaxing and enjoyable habit, something you look forward to each day. That’s why setting too many reading goals will be counterproductive. It will put pressure on you, and that’s the opposite of relaxation.