Additionally, at least for my use-case btrfs benefits me since it is less picky about drive sizes being the same and duplicating everything correctly - letting you essentially just throw additional storage at it as you acquire it.

Not all notifications go through FCM but all push notifications do as far as I’m aware - which is what the previous comment and the post title are talking about.

It is, in fact, worrying for privacy implications on the one hand and a real monopolizing factor on the other since if you wish to deliver an app which needs to implement such notifications you’re using Google’s service or constantly drain the user’s battery.

There’s UnifiedPush which tries to provide an open alternative but so far unfortunately still sees very little adoption.