If we wanted to go that way, then I'd go back to my original code order for - putting the '-X dev' setting first in sys.warnoptions, so both PYTHONWARNINGS and -W options override it.

Then https://bugs.python.org/issue32231 would determine the relative precedence of the BytesWarning filter. (I still think the interaction between "-Wd" and "-bb" is weird, but we can argue about that on the other issue).