* only simple CRUD apps - I've implemented with this type of stack a service similar to Parse/Firebase. I've also designed/implemented something like Basecamp+Freshbooks (in traditional PHP style, not a toy/demo app) and i know this type of stack can power just fine services like that (with a lot less code), i.e. your statement "simple CRUD apps" is not true

* monitoring - easily implemented in the proxy (can be as simple as $request_time in logs)

* multiple databases (I take it you mean read replicas) - tie each process (very lightweight process ... something like 5Mb memory) like this one to a particular db replica than use roundrobin in nginx upstream. So, to go from one db to multiple one you just need a different production config, no new code.

* use views/stored procedures to expose as an api then change your underlying tables (data storage format) to your hearts desire.

* Integrate 3rd ... - You are thinking/comparing tools like this to languages/stacks like php/node/ruby when infact you should compare them to things like active record. In traditional stack you don't integrate 3rd party at the same level as active record (in active record code), you do it either above or below this level. It's the same here only above means client code or (scriptable) proxy level (see openresty and njs) and below means database level (PostgreSQL is much more then SELECT ) or some worker process that reacts to system events that can be as simple as a events table or as complex as message broker.

SELECT * FROM reset_user_password() works in sql too