That's really interesting, I love the idea of being able to use columnar support directly within postgresql.
I was thinking of using Citus for this, but possibly using duckdb is a better way to do. Citus comes with a lot more out of the box but duckdb could be a good stepping stone.
Its a really handy tool. I've queried basically everything you can w/ duckdb - csv, json, s3 buckets, MS SQL servers, excel sheets, pandas dataframes, etc - and have had very few issues.