Yes, but you would usually have to read at least two columns anyway. What are the datasets that are too large to be ingested completely, but too small for a pro

Yes, but you would usually have to read at least two columns anyway. What are the datasets that are too large to be ingested completely, but too small for a proper columnar format? If ZSV is meant to occupy the gap between CSV/NLJSON (smaller datasets) and Parquet/DuckDB (larger datasets), this niche is actually really small, if not nonexistent.