Note: this is not about replacing ZooKeeper in general with Kafka as the title might suggest, it's about Kafka considering an alternative to its internal use of ZooKeeper:

"Currently, Kafka uses ZooKeeper to store its metadata about partitions and brokers, and to elect a broker to be the Kafka Controller. We would like to remove this dependency on ZooKeeper. This will enable us to manage metadata in a more scalable and robust way, enabling support for more partitions. It will also simplify the deployment and configuration of Kafka"