The ability to have custom initialization hook would be still very useful. In my environment, I have two JEE applications deployed onto a single JBoss instance. I have to differentiate logging config for each. Now, I'm bundling logback.xml in application, but I would have to load the configuration from external file (i.e. different for PROD and DEV environment). I can not use any global system property, since it would affect both applications. Perfectly, I would use the mentioned above logback.configurationClass property, to specify my code, which would implement required logic.