Embarcadero has released a patch to extend FireMonkey with support for Firebase Push Notifications on Android clients. The patch is available on GetIt as you can see below. 

The patch includes the required JAR files, the Delphi interfaces, and a snippet.txt file with code snippets for your application, both source code and manifest and configuration files you need to add to an existing or new application. 

We have also published a very long and detailed blog post, with all of the steps needed to create a Firebase project on the Google platform, instrument your application with the code from the snippets, and even test the resulting project. Hope this helps adding push notifications now that Google GCM is going away. The blog post is at:

https://community.idera.com/developer-tools/b/blog/posts/firebase-android-push-notification-support-with-rad-studio-10-3-1

For the future, as per the product roadmap, we are planning deeper integration of Firebase in FireMonkey, even beyond the Android platform.