Very bad idea for a base table, sure. OTOH, potentially great idea for a (possibly materialized) view (as might eagerly storing an array of row values instead of keys.)

> Storing binary files as base64 encoded strings in text columns

That might not be a bad idea depending on size, and depending on how often you needed the binary vs. a base64 encoded string: if most of the use of the binary is in a context where it will be sent as base64 encoded, storing it that way might be a great idea.

> Using a table with `key` and `value` string columns instead of using redis

If you need an in-memory cache, sure. Otherwise...you could use redis, but I’m not sure why it would always be preferred.

> Pub/sub using NOTIFY/LISTEN - Message queueing

NOTIFY/LISTEN are a pub/sub mechanism. You shouldn’t use them alone as an application level message queueing system, but you definitely can build such a system on PG and might well use NOTIFY/LISTEN in the implementation.

> - Storing executable code

There are probably problems that involve specific instances of doing this, but this is at best to general to describe a thing yoi shouldn’t do.