There are a few bane items in the game, but they are sparse and hardly used. I've always liked bane items in general, and think it would be cool to add bane focuses (humanoid, undead, summoned, elemental etc) to more weapons. Similar to lighting effects, this is probably not something the staff routinely considers when designing items, but it's a great way to add more personality to the wide assortment of generic damage weapons floating around.