An interesting number would be how many GCM/APN devices are registered in the matrix.org sygnal server.

All of the Matrix/Riot users I know use private, non-federated home servers, but still rely on the project's Sygnal server(s) for push notifications.

Sygnal doesn't track this, actually. The best figure i have is that right now the matrix.org HS has 125,209 registered pushers - but as sygnal doesn't store registrations in its DB, I don't have an easy way to say how many Riots on other homesevers are routed through it.

Phone number/email verification is also still centralized as no one has worked out any other way.

Only to the extent that identity servers themselves are centralised, and Matrix lets you run your own.

Important to note you're not required to use any of these features....considering sign up takes 7 seconds within the app (and for security... Email is a weak point), I bypassed it.

Both are a weak point, when it comes down to it.