[sspiff]

This also blocks me from using TextSecure/Signal, because they require Google Play Services at run-time.

I'm using a BlackBerry OS 10 device, which can run Android apps, and I even have Google Play running on it, but Google Play Services is stubbed for a large part on BB10, making some apps (such as Google Maps, Google Calendar, and Signal) impossible to use.

Why a security/privacy oriented application such as signals wants to bind so strongly with Google's services, I don't understand.

[pureIDEOLOGY]

They want more users. Google actually makes special deals with carriers to optimize GCM, so it's best for battery life. It depends on your carrier, but the websockets fork LibreSignal can use up to 5x the battery life. On my phone using the fork bumps battery usage from 1-2% to 2-4% (Sprint), but is totally worth it to avoid Pentagon/Alphabet (I mean Google).