[SahAssar]

If you're transmitting two streams you use two streams to transmit. I don't see the problem?

[amelius]

Two streams over the same channel.

[SahAssar]

I don't see why this is a problem with ndjson anymore than it is a problem with other stream text encodings (like CSV).

ndjson seems to be about how to format the content of the stream, not about how to multiplex multiple streams over a single channel. Use http2, zeromq, raw tcp or whatever else you like for that.