> ^ To me that is an obvious clue that this is not something that you can standardize. The message interfaces make sense (and appropriate) but the *FactoryInterface files have no business being part of something that's "standard" IMO.

Are you saying there shouldn't be a `StreamInteface` or there shouldn't be factories? Or both? I absolutely think there should be a StreamInterface for message bodies. However, I am open for suggestions on whether or not the factories should be part of the PSR. What are the alternatives in your opinion?