In terms of using stderr/stdout: yeah I think this is totally defensible. And depending on how hard you squint, and if you use Plan9, logging to a separate log

In terms of using stderr/stdout: yeah I think this is totally defensible. And depending on how hard you squint, and if you use Plan9, logging to a separate log file is just a metrics stream too, and it very well could be transformed into one before being sent anywhere else. This is overwhelmingly normal too, so it's not a hypothetical extreme at all - avoiding std* is often a good practice. Semi-structured streams with basically unbounded cardinality are still useful tho, and I think that's arguably "a log" regardless of how it's represented. And then levels come back into the system.