Trazan. No because it would not be a global setting. And monitor out still is not stereo. Furthermore i like to have a bit of headphone space in the in ears but not on any other outputs. Så the scaleable volume should be on the headphone jack.
you are correct that rig volume does not always equal loudness BUT if you are very experienced with guitar setups and know what you are doing (as i do) it will get you very close to perfect. And though scalable volume on the headphone out might not be scientifically correct it will get me very much in the ballpark. And in ear playing comfort will be MUCH improved.
to the team. 500€ i will donate to your christmas lunch if you code this feature. NOT kidding!!!