Sorry, that was my question-- was there a way to avoid using librdkafka's threadpool and essentially use it as a 'dumb' client, moving all the async stuff to your Pony actor layer?
I'd imagine that the internal thread pool for sending/receiving data from Kafka is as core to librdkafka as the internal thread pool for running actors is to Pony and trying to remove or disable either of them would be a large undertaking.