> If all business happens in one transactional system, your semantics are dramatically simplified.

100% agreed. One of the biggest issues SQL databases have faced is that the scope & scale of "one transactional system" has evolved a lot more quickly than any off-the-shelf database architecture has been able to keep up with, resulting in an explosion of workaround technologies and approaches that really shouldn't need to exist.

We're now firmly in the cloud database era and can look at things like Spanner to judge how far away Postgres remains from satisfying modern availability & scaling expectations. But it will be great to see OSS close the gap (hopefully soon!).