Agreed, cyclomatic complexity is definitely something to be aware of when designing functional programming systems.

Although, I disagree about Clojure's readability, but that's probably because I've been doing it for so long.

Interesting Java project you've got there. Reminds me of Clojure's core.async library and software transaction memory ;) (though, I know it's not exactly the same thing).

If I was transforming large streaming input from Kafka or Kinesis, I would probably reach for Cortex (a map-reduce style lib for Clojure), or I might rig up some strange, stream-to-lazy-seq adapter and reach for transducers as they have much better performance when dealing with larger input.