Didn't old-school blackboard systems sort of evaporate into a modern combination of a persistence layer, a task queue, pub-sub, and bespoke code for evaluating/scheduling/executing tasks?

That's not really what I was referring to. I meant more of a system of working assumptions (call them first-class axioms, propositions, facts, whatever) that govern behavior and can be updated when observations occur that contradict them -- not a task queue or a database of all known facts. Sort of like human core beliefs that dictate how we see the world.