Google has launched Cloud Pub/Sub, a massive scalable messaging platform. I think this can and must replace GCM and maybe even MQTT. For developers without enough server capacity Cloud Pub/Sub could be a very good solution.
it seems it's still a beta project full of warnings about too many elements that will change in near future or are not implemented as of today.
If you didn't before, have a look at PushBullet, a framework that delivers today most if not all of what BigG will surely do on a larger scale tomorrow.
BTW, @DonManfred and I are working on a class/library for PB (it's almost done).
Yes, you're right.
Me too am not happy to have their app to receive pushes and at times fantasized about discovering the intents used in order to write a "receiving" app by myself just to acquire full control. Obviously there are so many other ways to achieve same goal (push messages) that putting time and efforts on the subject may be useless.