Messenger chat and Instagram Direct are now integrated
| "We're connecting the Messenger and Instagram experience to bring some of the best Messenger features to Instagram - so you have access to the best messaging experience, no matter which app you use." |

Image source: Facebook
Facebook thinks having lots of messaging options can be confusing, and the solution is to bring all messages into a single, unified platform.
If I recall correctly, Microsoft also implemented a similar concept in Windows Phone 7 and earlier iterations of Windows Phone 8, with Facebook Messenger smoothly integrated into the native messaging app.
Anyway, Facebook's ultimate goal is to have all three of its messaging platforms (Messenger, Instagram Direct, and WhatsApp) connected together without downloading each app separately. However, all your existing Instagram messages and call details will only be available in Instagram. The announcement also didn't include WhatsApp yet, as Facebook's Alexandru Voica explains:
| "Right now, we are focused on cross-app communications Messenger and Instagram. We are still determining how cross-app communications will work with WhatsApp. WhatsApp will continue to remain a separate, end-to-end encrypted app at this time." |