Boring answer: more empathy. This world seriously needs so much more of it.
Fine. Be boring. But also... no.
Empathy is a dangerous emotion. Empathy is thinking you know what is right, Empathy is a mother not letting their child find their own way. Empathy is the American government banning rock music in the 60s. Empathy is believe in the greater good. And the greater good is heresy. (pardon my Warhammer)
If the world was more empathetic, I would not be down here to discuss it with you. But I digress. PM me if you want to discuss this further. I don't want this post to become even more politicized.
I don't like mental changes. It makes me feel... icky... inside. But if I was to change the human experience, I would remove all potential for people to become pedophiles. No more Loli. Not more age-regression. Nobody would ever be, or could ever be, turned on be pre-pubescent children.
I could see sadism becoming the work around. With the arousal coming from the physical act of hurting a child rather than the child itself. I'm not condoning such an act, I'm just following out my own train of thought and the rules I set. Child abuse is the worst thing a person could do outside of mass-genocide or not vaccinating your kids.
Hot Answer: Everybody gets secondary faces in their groins. Complete with cock-tongues and pussy-mouths. Plus, a small baby-bulge to store a second brain just in case the primary becomes damaged.
"Nothing gets me going like good world building"