Well, Google has confirmed that it will have four messaging applications in its roster. Remember that both Hangouts and Messenger can handle SMS texts while both Allo and Duo, said to use your phone number for identification, may also integrate texting as well. Duo, a dedicated calls app, competes with Hangouts in that aspect.
Sure, feature completeness varies across the line with Messenger being a barebones app while Allo and Duo representing the deep end of WhatsApp and WeChat with Hangouts being a happy medium. But maybe four apps is a little too much.
It’s possible that we may see Hangouts and Messenger switch out features when the two new apps debut this summer. It may also be that the older apps will get a slow phase-out.
Source: Android Police