Android itself may be open source and ready for any mobile device maker to use, but the Google apps are a whole different story. If you want the Play Store on the phones you make, then you need to play ball with Google - and, among other things, agree to preinstall a certain list of apps. This changes from time to time, and come December 1 it will change once more. From that point on, Google Duo will become a mandatory preinstall for Android phones, replacing Hangouts in that role. Hangouts will be an optional preinstall, meaning some manufacturers may choose to ship it with their devices,...
Source: http://www.gsmarena.com/google_duo_will_replace_hangouts_as_a_mandatory_preinstalled_app_on_android_phones-news-20953.php
