For an installation with hundreds of JNLP slaves it becomes difficult to ensure that the slave.jar agents get upgraded when there is a significant change to the remoting layer. It would be nice if slave.jar detected when it was out of date relative to the current version available on the master, and tried to swap in a new version. On Unix slaves (uncommon for JNLP) this could be done just be replacing the file; on Windows slaves it would be hard since the file cannot be rewritten in place. Either some JNA code like in WindowsServiceLifecycle could call MoveFileExA(..., ..., MOVEFILE_DELAY_UNTIL_REBOOT | MOVEFILE_REPLACE_EXISTING), or the service wrapper could be instructed to look for a JAR update.
Failing this, there ought to at least be an administrative warning if one or more slaves are running an outdated agent.