I would like to see blood bandits coming back.
I actually loved the time where people would stop people on the streets, just to steal some of their blood.
I think this could be done by making blood test kits less rare. Also I would change it that you can't take blood from a dead person, this makes it so that you won't be killed on sight for some blood. Unconscious players should be able to give blood though.
Maybe even make it harder to regain blood?