I checked it out but didn't see any new settings. Maybe it's still in-progress? I even tried manually setting the buttons on the Pro Controller with the gamepad as controller 1 but it didn't work.
Did you make a brand new build of RetroArch to test that? Or are still using a version made before that PR was merged yesterday? Depending on the answer, that could explain why you saw no new settings. (As an FYI, 1.9.5 did not release with that option added in)