I would like to keep my hairstyle when I equip some hats or helms. I hate how your character goes bald or with very short hairs when wearing them. For the helm you could have some hairs coming out from it when you use a long haircut, Valkyrie Helm and Helm of Neitiznot come to mind for this. You already have Eir that has hairs coming out her Valkyrie helm while our model just act as being bald. I'm sure theres a way to get the hair model of Eir for most of the helms when you use long haircuts.
Runelabs Skilling/Combat Bosses idea