I've heard of it being used as a sort of message queue for application level events before, but that sounds like a nightmare of trying to reinvent the actor model with 1000x the complexity.
Just like SOA and ESB, the concept isn't the problem, is the technical constraints of the design at the time. Decoupling and messaging isn't bad, but having a legacy message queue on physical hardware doesn't really hold up. Any derived architecture faces the same problem.
Then again, Kafka isn't an actor model implementation, and Akka isn't a partitioned redundant stream processing system, they don't have all that much overlap ;-)
Not saying Akka can replace Kafka but many of the issues around availability, durability and reliability have been attempted to be solved in Akka.