>I agree that a streaming response is cool, but why the dismissal of returning valid JSON, streamed?

JSON hasn't been designed for chunked interpretation. How would the client know when to start interpreting the received message? How could you tell the difference between a valid chunk or malformed response?

>With this new-line-delimited JSON format all your clients HAVE to know about your new protocol

Yes. It's probably not a good option for public. It should be a complement to a more general API. I would put this in the bucket of micro-optimization for very specific use-cases. Regardless, if you publish your API and document it, other developers should be able to consume it just fine. It's not rocket science.