One way communication

The most recent question specific to this issue is five years old, so I’m asking again: Is there a reasonably easy way to configure Openfire/Spark to disable users from communicating with each other and only allow a few people to send broadcast messages? We would like to use this as a notification tool for system issues and possibly as a backup for emergency notification as well.

No. Openfire is designed to work as a two way communication tool (chat). You probably need a specialized solution for that. One can try to achieve that with Packet Filter plugin, but i won’t call it reasonably easy and convenient. Also, having chat client running all the time just to receive an occasional message sounds inefficient and weird to me.