Networking
It would be nice to have a networking system, where users can exchange diaries or even simpler: Adding Friends / Users / Community. Or for example, intergrate to list all users who use the app ( optional to be seen or not ) and, you can mingle that way.
A way to network with others, because as you know it Diaro is one of the most efficient apps I worked with, and a lot of people use it for different things. Imagine if, you can expand those uses to reach out to others such as a support group ( people with anxiety-etc ).
Maybe, this app can start off with the basics for now, and add a mood option where you can just have an entire different header for the moods.