Not sure how possible it would be for the devs to implement this, but I would like a separate equipment slot for the face. That way glasses and eyepatches, etc can be worn with hats. This could even bring about a whole new type of facial accessory, such as pipes and other things to wear in/on the mouth. For reference, consider how Ragnarok Online does it. This would be wonderful for RPers and some facial accessories could also have special stats and abilities, or even effects (a smoking pipe, for instance).

As for head armor that include both a hat and eyewear already i.e. scholar gear and helmets, simply have that armor take up both slots, much like the hooded body armor taking up body and head.