For cases where JENKINS_HOME is located on e.g. NFS or a SAN, as the exploded plugin directories are really a redundant copy, it would be beneficial to be able to relocate these outside of JENKINS_HOME (much like the --webroot parameter allows relocating the extracted WAR file directory outside of JENKINS_HOME)

Most likely the only way to implement this is as either a system property or a CLI parameter as by the time Jenkins has started up it is too late to change the configuration option.

Additionally there is the use case where the JENKINS_HOME is on a redundant file system in case of disaster recovery, so the target extraction directory may vary depending on which node in the DR is being brought on-line, so it does not make sense to store this in a configuration file (as there is no guarantee that the mount paths are the same, etc)