Cool thing about DuckDB is it can be embedded. We have a data pipeline that produces a duckdb file and puts it on S3. The app periodically checks that assets etag and pulls it down when it changes. Most of our DB interactions use PSQL, but we have one module that leverages DuckDB and this file for reads. So it's definitely not all-or-nothing.
Are you using pg_duckdb to embedded it inside postgres and access it via psql or other pg clients?