The PRPC logging is done with Log4j. Since there appears to be a kafka log4j appender you could update the prlogging.xml and define your own appender to go to a kafka topic. You would need to make sure the kafka appender java code library is part of the JVM classpath in a way that it can be properly used. Most importantly please make sure the appender type is using async requests. (These network type appenders do scare me a little bit)
Not sure I know of anyone who has done this before with Kafka but updating the prlogging.xml and changing/adding appenders has been done.
Currently we have done whatever has been mentioned by Chris above and one of the major hindrance we have now is our Pega 6.1 server supports only Java 6 which in turn can support only kafka 8 or below. Unfortunately our host system where the actual kafka server resides uses kafka 9 and also has kerberos security adopted.
I'm not much aware of these acronyms but what i was kept informed was that the apache kafka 9 version and above have ootb jaas configuration that would allow us to log messages through kerberos whereas the lower versions dont. So finally we are now put in a position where we need to create custom code to aid with jaas.