I just sent an email off to one of the syslog-ng developers to see if they have support for this...
http://tools.ietf.org/search/rfc5424#section-6.3
.Seth
Apparently syslog-ng does support this. That will have to be another option for the syslog writer in the "to be written" logging framework. Syslog-ng can actually output to various databases too so it actually might make sense to implement a syslog writer with key-value support early on in the process so that people can start outputting to databases without us even needing to implement database writers.
.Seth