Why would you need this? Who store states in-memory in a web app? It will always limit you to one app instance, and it's not like there's a shortage of state saving alternatives..
The in-memory state is a simplified example for the purposes of demonstration, but there are plenty of debugging scenarios where you're trying to track down a problem and for whatever reason have a hard time reproducing it locally. This lets you sidestep the whole issue.
if you want to change configuration data remotely without a restart, and don't want to use jmx. you'd still need to persist the change or else it wouldn't when the service restarts.