Thank you for looping me into this conversation. I’ve worked around the way that rclone has used stderr, but I agree that only errors should go to stderr. In my familiarity with the command line, output that is reporting stuff (for example the check command) has typically gone to stdout.
The way I use the check command is to redirect the output to generate a status email. Having that go to stderr means I have to add 2>&1 to the command, which is fine just unconventional.