Note that this only affect binding with Lo4J 1.x as per https://github.com/qos-ch/slf4j/blob/master/slf4j-log4j12/src/main/java/org/slf4j/impl/Log4jMDCAdapter.java#L37

For Log4J 2 the binding is with the Log4J project and is differently anyway: See https://git-wip-us.apache.org/repos/asf?p=logging-log4j2.git;a=blob;f=log4j-slf4j-impl/src/main/java/org/apache/logging/slf4j/Log4jMDCAdapter.java#l46