In the URL https://developers.google.com/cloud-messaging/ there's this messade:
Firebase Cloud Messaging (FCM) is the new version of GCM. It inherits the reliable and scalable GCM infrastructure, plus new features! See the FAQ to learn more. If you are integrating messaging in a new app, start with FCM. GCM users are strongly recommended to upgrade to FCM, in order to benefit from new FCM features today and in the future.
GeneXus already supports FCM? Is it planning to support?
I'm currently using Ev3U8.
No, GeneXus 15 RTM and previous versions don't support it natively yet. There are plans to support it in upcoming upgrades.