[throwaway7783]

I don't know. For me, I need

* a primary transactional DB that I can write fast, with ACID guarantees and a read-after-write guarantee, and allows failover

* one (or more) secondaries that are optimized for analytics and search. This should also tell me how caught up the system is, with the primary.

If they all can talk the same language (SQL) and can replicate from primary with no additional tools/technology (postgres replcation for example), I will take it any day.

It is about operational simplicity and not needing intimately to know multiple technologies. Granted, even if this is "just" postgresql, it really is not and all customizations will have their own tuning and whatnot, but the context is all still postgresql.

Yes, this will not magically solve the CAP theorem, but for most cases we don't need to care too much