How is this different from Firebase RTDB? And perhaps more importantly, does it address the scalability and consistency issues associated with Firebase RTDB? Google introduced Firestore to Firebase specifically because RTDB has limited usability for larger real world applications that go beyond "sync device state to DB".

Even the offline first paradigm is fundamentally flawed in general and certainly when it comes to offline data manipulation. Either you can afford to mutate your data on the local device and sync it when possible, in which case you clearly don't need subscriptions to real-time mutations of remote data because within that scope you are the source of truth. Or, you're interested in mutations of real-time data from multiple clients in which case you need to deal with conflict resolution (mutually exclusive changes of data) which is not reliably possible with this model and scalability (linear increase in pub/sub * increasing query cost = exponential scaling).

Are there any large projects or companies that currently have this in production?