According to a few leaked screenshots that have surface online, WhatsApp may be planning to enable data sharing with Facebook so that both services could possibly offer a few more additional features and improve the service. At the same time, it is also possible that Facebook may use user data collected from WhatsApp to serve more relevant advertisement to those users on Facebook. WhatsApp recently announced that it would no longer charge a nominal annual fee and instead would be “lifetime free”. In addition to data sharing with Facebook, WhatsApp is also apparently planning to introduce a feature that would tell users when their messages are end-to-end encrypted and when they are not. The feature, at least for now, is said to be off by default and if a user wants to utilise he or she will have to turn it on.
It is clear that majority of WhatsApp users are also on Facebook. By utilising the data from WhatsApp, Facebook may personalise the timelines better for users by showing them posts from their close WhatsApp friends on priority. Currently, there is no clarity on how and why WhatsApp would share its data with Facebook. Although the move could be controversial. While Facebook owns WhatsApp, it is an entirely different service and some users may raise the privacy issues around the data sharing, although the feature is likely to be optional. It is also not clear how Facebook would use this data. Though, some scenarios can certainly be guessed.
After all, such integration between services to serve ads has already been pioneered by Google, which takes into account almost all the data users have across its various services to serve them relevant and timely ads. Both the data sharing feature and the encryption signal for chats would be likely offered to consumers in the next version of WhatsApp. Currently, they are part of a leaked build of the chat app.
Facebook and WhatsApp are sharing data since the day the latter was bought by the former, that's an open secret. This is also the reason why many people switched to secure messenger like Threema and Wickr.