Author here. This was an unusual setup. The database server is directly accessible to users but they were only given INSERT and SELECT privileges on the table. The users need flexible querying with SQL so that they can use existing BI tools like Metabase.

This system is minimal, is running almost perfectly and has > 100 happy users. There isn't sufficient justification to introduce custom code layer and break all the existing functionality.

pgcrypto already does support PGP encryption after all, just not ECDSA.