I've been hearing a lot about much heavier blocking and opt in federation. If I were to predict how it all ends up, I see 10-100k users on a small group of servers siloing themselves, and the rest of the fediverse remaining as is. Or even opening up more than it is currently as the loudest people calling for it silo themselves away from the rest of the fediverse.
I won't say that one particular model is against anything or wrong, the point of free software is the freedom to use it in the manor preferred and if people get value from a walled garden then more power to them. Just not for me.
On notifications if Google play services is not installed unless the app let's you configure another server to use in place notifications won't work that use Google Play services installed on the back end.
If sandboxed Google play services is installed, assure it has the neccisiary permission to run in the background (unrestricted battery and network) access. Not just the individual apps, but the google apps specifically as Graphene installs thegoogle stuff with standard permissions.
Same goes for apps that run in the background. If you expect them to be running in the background to auto update or perform another function then it needs to be permitted in the battery settings. Background updates may also rely on Google Play services.
Edit: to clarify I haven't experienced any issues myself that weren't directly related to my decision to not use sandboxes google play services (no push notifications) despite daily driving for years. It's a particularly old and reliable project in the privacy space, and while I'm sorry you experienced issues that doesn't make it an unstable project not ready as a daily driver (any more that somebody having issues with Windows/Linux makes those unstable and not ready to be daily driven).