I love WhatsApp. It is the primary way I stay in touch with my family. However, there are a few things I think it could and should do better, three of which I hope to address with this project.

Re-Tweeting is the embodyment of being told something and sharing the information with other people who might not have it yet. This is especially useful in a digital network that consists basically of groups that are invite-only. WhatsApp is not doing a great job at it currently, it takes four taps to re-share.
The proposed interaction tries to minimize the effort. It totals at one long-press and sliding your finger across the screen

Seeing who saw what in a group is something no messaging app has gotten right yet in my opinion.
WhatsApp only shows read-confirmations in conversations of two people via an extra checkmark. Facebook's Messenger displays text, and others like WeChat are avoiding the issue altogether by not displaying any read-information at all.

In my proposal the read-configuration and online-status use the same metaphor of circles that are either outlined or solid.
In the status bar (at the top of each chat) an outlined circle means the user is offline, a full circle indicates the user is online. The names next to the circle associate the group members with colors.
In a message-bubble you sent, the circles replace the current checkmarks. An empty circle means the user hasn't seen the message whereas a full circle indicates the person associated with the color has seen it.

The status bar allows for up to 5 people (groups of 6 including you) to be displayed along with their status circles. In my research I rarely found groups with more members than that, however, in groups up to 50 people the read-status could be moved to the conversation details, accessed by tapping the status bar at the top of each conversation.

In Social Media, everything is about sharing. The idea of a diary is the anti-thesis to that. Sometimes I want to keep things to myself, or just store them for sharing later.
In this case items are saved to iOS notes (which also supports pictures since iOS 8), but the diary could also be part of WhatsApp or a standalone app.

The concept also shows an UNDO feature for quick actions like deleting. I'm not sure if there are architectural reasons this has not been implemented in any other delete action in iOS (that I'm aware of) but to confirm every single foto I want to get rid of drives me crazy.

You can go ahead and try the prototype yourself on an iPhone 5/5C or 5S. It is limited, but should give you an idea how this sort of interaction would feel.

Thank you Li, Matthäus, Abi, Dani, Roland, Laura, Christoph and my siblings for lending support, tripods and cameras.
Also, I couldn't have built it without checking StackOverflow more than I can count.