Have you looked into something like BPMN + DMN? BPMN provides workflow modeling and basic decisions, and DMN provides decision tables which can implement more complex rules. There are a couple frameworks which can work on top of that to provide a system implementation.

Exactly this is what I was thinking. We currently have a workflow engine that is event driven + a projection (think: CQRS), and it’s fairly unwieldy. Most specifically, the business logic is defined all over the place, and I was wondering whether a rule engine would make it easier to define the constraints and business logic to act upon these events.