The Facebook CEO and founder Mark Zuckerberg, last year announced that it plans to merge three Facebook-owned platforms, which are Facebook, Instagram, and WhatsApp. The aim is to provide cross-chat support.
It seems that Facebook has started giving codes that will permit Facebook Messenger to have cross-chat support with WhatsApp. But as both platforms are based on different concepts, it would be difficult to integrate them.
It is pertinent to mention here that WhatsApp only allows users to store the chat info on-device and also has end-to-end encryption. Thus it can be used just on one device at a time. On the other hand, Facebook Messenger stores info in an online database. Users can send messages and receive them on multiple devices at the same time.
Initially, the report regarding the integration of WhatsApp and Facebook Messenger was reported by WABetaInfo reverse engineer @Alex193a. He reported that there are new tables in the local database to manage messages, services with other WhatsApp users. The tables will enable Facebook to access the WhatsApp users blocked list.
Even though the content of the message can not be shared with Facebook servers, the social media giant would have to upload the local database to sync it across all devices.