thinking out loud…if lakeFS UI will show the contents of a CSV file that's been added, could it also do the same for a parquet file that's been added using the same duckDB-powered viewer that's available in the main object view? I get an actual diff on a changed file wouldn't be possible, but if the file is brand new it might be nice for the user.

That's a valid point! However... the majority (I believe) of systems that read/write Parquet follow the hive conventions that typically care more about partitions - in which case, removing a record translates into dropping a parquet file in a prefix, and adding a differently named one into the same prefix. I agree that the simple case where I only added a file would be easier, but it's not enough to look into the file itself - we'd also need to look for deletion of neighboring files to know whether it's an addition or update (and actually scan both).