Most of the Freemium options seem to be targeted at either (a) mobile apps or (b) enterprises (their homepages clearly target executives/managers, not developers). They seem to want to own your whole stack. We have an existing app, with just a small bit that needs to be realtime. Firebase is the perfect solution, so it's really a shame that their future isn't bright.

As for the open source solutions, I specifically want to pay someone money to solve this for us. We've been running ShareJS, but it's annoying to maintain and fix.