Creator of Arroyo here—we agree that stream processing is a different beast and needs different infrastructure from a batch engine like DataFusion.
Our approach has been to take pieces of DF (including the SQL frontend and expression engine) but embedding them in our own dataflow and operators. This allows us to support low latency, distribution, watermark processing, and consistent checkpointing.
But the great thing about DF is that it’s designed as a toolkit for SQL-oriented data processing, so it’s relatively easy to pick and use just the pieces you need.