I think something that would be really neat is if Headgear were broken up into two compatible groups (though I imagine this might effect load times, so I'll understand if it isn't). But I'd sure like to be able to have glasses, and match them to various hats.
Sometimes, particularly when you find yourself going to hell a lot, or partying, sunglasses are a necessity.
Also, I'd love to be able to wear a masquerade mask and a pair of horns at the same time! o.O
In any case, this would allow for another level of personalization for that truly unique look.