When you get around to updating pain modifiers - I'd suggest increasing the pain receptors for eye tissue.
Even the toughest creatures on earth are overcome by eye wounds, and right now DF treats it the same as a skin injury.
Aren't faces targeted unusually often in DF, though? Hitting eyes IRL is pretty difficult, but this isn't really reflected in DF's combat. I care about balanced combat more than I care about realistic eye injuries. I'm thinking of one of my favourite features from Grimlocke's mod, which shrinks the size of cheeks, eyelids, tongues, and lips to keep them from being targeted often. I can't imagine eyelids, lips, and cheeks are targeted in melee combat as often as they are in DF, and eyes are probably similar. It might be worth while to do some solid arena testing to see how often they're actually targeted. I'd hate to introduce yet another "common injury that halts combat earlier than it should" right after the release that supposedly fixed most of that.