I've used Firebase for a couple internal company projects (right after they left beta) and I was able to quell any misgivings our AMs and PMs had about relying on 3rd party startup services by explaining the sheer amount of time saved by not building their functionality ourselves.
I've been holding back on using it for client work as the same people can't get past "only a year old service so not ready for production", but now with Google's backing and them making it clear it's not just an acquire-then-abandon startup I have more ammunition to sway pessimistic minds when a Firebase backend is warranted.