We know that Facebook eventually plans to integrate WhatsApp into Facebook’s other apps. As reported by WABetaInfo, reverse engineer @Alex193a has discovered evidence of this in the latest version of Facebook Messenger. The list below shows the mentions of “whats_app” references.
This could be a pre-cursor to the long process that it will be to integrate Facebook Messenger and WhatsApp users. The main difference between both messaging platforms is that WhatsApp stores chat information on-device in addition to end-to-end encryption (along with the ad-free experience). This is why WhatsApp is only allowed to be used on a single device.
The references point to the creation of tables in a local database on Facebook messenger, which are needed in order to manage messages and services. There are also mentions of other elements that would allow Facebook Messenger to understand which WhatsApp users are blocked, push notifications from WhatsApp, and the details of a chat recipient.
The content of the message wouldn’t be shared with Facebook servers. Thus, the Messenger app would need to incorporate a new protocol in order to cross-chat between Facebook Messenger and WhatsApp. It isn’t known if Facebook would upload this local database in order to sync it across devices – one characteristic of Facebook messenger is that you can send and receive chats from multiple devices simultaneously.
We should remind you to take this story as speculation, as app developers are subject to change plans down the road.