I've implemented basic include file/directory functionality in syslog-ng, using the format numbered second in my previous post.
I've now pushed an expermental implementation of include files in the syslog-ng OSE 3.0 repository, in a separate branch called 'include'.
E.g. in order to test the code, please clone the syslog-ng 3.0 repository:
$ git clone git://git.balabit.hu/bazsi/syslog-ng-3.0.git
Then check out the 'include' branch:
$ git checkout --track -b include origin/include
Then compile as usual. I didn't want to integrate it right into syslog-ng OSE 3.0 tree as I'd like to release that first as 3.0.1.