Re-reading this RFC I am somewhat surprised that there is nothing between INFO and DEBUG. For Starlink applications INFO was the default and DEBUG was for lots and lots of detail that you would only ever turn on if you wanted to be swamped because you were trying to sort out a problem. We had a VERBOSE option for information that was useful some of the time (for example, showing how an algorithm was converging) and for production runs I always enabled VERBOSE logging. It was definitely true that the default command line output of tasks was INFO and that people got annoyed if running a task generated pages and pages of output by default.
I worry that moving the default to WARN means the the log files will be mostly empty without any feedback at all and general users will then want to re-run with INFO enabled (and be potentially swamped), but keeping it at INFO means we'll add more and more output there that might be useful for production but won't necessarily be useful for the general user.
I also understand that adding a whole new log level may just be moving the goal posts.