For the first problem, union types are the clear answer (abstract marker classes can approximate it somewhat). The compiler guarantees that all sent messages c

For the first problem, union types are the clear answer (abstract marker classes can approximate it somewhat). The compiler guarantees that all sent messages conform to one of a list of possible valid message types. If the subscribers are static, the compiler can also guarantee that every valid message type has at least one handler; if the subscribers are dynamic, you're treading much more dangerous waters but at least you have a comprehensive list of possible messages to verify at runtime that each one has at least one handler. For the second concern, I agree but I would invert it: if a publisher writes messages intended for a particular recipient, that's a misuse of a message bus. You'd be better off making a regular method call in that case (nobody says the bus should solve every one of your problems). Ditto for the third - if you absolutely need a specific response to your message, don't use a message bus to send it. The challenge of message-bus-based architecture at that point becomes minimizing the number of publishers which need to make direct calls.