Honestly, I never really liked the idea of a genocide snowdin papyrus fight. I think it makes the human look more redeemable. In the original undertale you're considered to be actively hunting down monsters after snowdin, that's why the enemy encounter sprite changes from suprise to happy. This is because you could argue that every single kill this human has done "could" have been self defense. Every monster poses at least somewhat of a danger in your battle with them, but then papyrus doesn't even fight you, he just walks up and hugs you and so by you killing him. There is no arguement to self defense anymore. And I think if you would have a battle with him it would be a bad idea since you could argue that everything in the game is self defense since papyrus is the only character that spares you before you even fight.