I'm sure this would be an easy add-on. There will probably be quite a few mods for this on release also. Personally i prefer more realistic haircuts instead of everyone looking like they came right from the hairdresser. Short, long, none. But who cares.
It depends on the character and class for me.
Fighters and Rangers I tend to give short and sensible haircuts, or at least tied back. Wizards and Clerics I'll go with either elegant and elaborate or long and mystical. Rogues and Warlocks get whatever I apply to their concept, from elaborate con artist to scruffy urchin and mad zealot.
