But in rules you already have barrier free access to Things in the rule through the ThingRegistry. In the UI they already have access to the Things status in the Things menu of MainUI. To trigger rules, at least in the UI and JSR223 and GraalVM rules languages you can use a GenericEventTrigger to get something akin to a “Member of Group changed” type trigger for Thing status (see the link in my previous reply for an example).
I’m still not seeing what reflecting the Thing’s status in an Item really buys you. I can be convinced, I just don’t see it right now.
If you are talking about MQTT Event Bus [4.0.0.0;4.9.9.9], let’s move the discussion over to that thread to further explore what can be done. The OH MQTT binding itself doesn’t natively provide an event bus implementation.
But if that’s the case then no, it’s not obvious that some values are not sent even if changed. As I’ve implemented it every update gets published to the state topic as a retained message, whether or not the update reflects a change.
If you are talking about something else, well it’s going to be up to what ever that something else is to implement some sort of messaging protocol to republish a device’s state, in which case that would be reflected in a Channel on the MQTT Thing and the standard Item interface.