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- I don't think the restriction to *async* message passing should be a stated requirement. Synchronous message passing (such as CML channels) for in-proc communication  provides a degree of determinism that can make debugging and reasoning about the code easier. Communication across process boundaries *should* be async but I don't think the two are at odds with each other. Async across the board does result in a more uniform model, but I think room should be left open for carving out determinism where possible. 

- Non-blocking seems to be a low-level requirement which doesn't need to be addressed in the manifesto itself. Non-blocking is an assumption of systems based on actor model, but in declarative models of concurrency, whether something is non-blocking is left up to interpretation.