Why do we not have a Magic Damage Destruction Staff? It would not take a lot to add to the game and the only thing to worry about would be what it could offer over the other staves. This could simply be addressed in the passives. For Example:
Tri Focus:
While an Arcane staff is equipped your Magicka Recovery is increased by 10%.
Ancient Knowledge:
Arcane Staff increases the damage you deal with Direct Damage abilities by 8%.
As far as the aesthetics go you could give them a unique appearance that reflects their tooltip icon. Perhaps a purple look.