TL; DR: The pandas and dask backends are being deprecated and will be removed in version 10.0. DuckDB is the default backend for Ibis and is more performant. The pandas DataFrames will still be available for data transfer, but using pandas to execute queries will not be supported. Dask is recommended outside of Ibis. Originally, Impala was the only backend, but Postgres was added due to adoption issues. The pandas backend was used as an in-memory DataFrame engine, but it does not align well with Ibis’s deferred execution model. The pandas backend is slower and has more specialized code than other backends. Ibis prefers NULL over NaN for missing values. Dropping the pandas backend is justified due to DuckDB’s feature parity and performance.
https://ibis-project.org/posts/farewell-pandas/