Facebook is currently working on integrating its three chat services - Messenger, WhatsApp, and Instagram. They won't merge, continuing to function as standalone apps, but their owner wants their users to be able to message each other across platforms.
In order for this to work a huge amount of reconfiguration needs to be done by "thousands of Facebook employees", according to a report from The New York Times today. They will need to change how the apps function at their most basic levels.
Mark Zuckerberg's goal is for all three apps to incorporate end-to-end encryption once the integration is complete in late 2019 or early 2020. Currently WhatsApp has end-to-end encryption on by default for all conversations, while in Messenger you can opt into end-to-end encrypted chats.
In a statement, Facebook says it wants to "build the best messaging experiences we can; and people want messaging to be fast, simple, reliable and private". The company is "working on making more of our messaging products end-to-end encrypted and considering ways to make it easier to reach friends and family across networks. As you would expect, there is a lot of discussion and debate as we begin the long process of figuring out all the details of how this will work".