Sacred killing weapon

[Lingchih]

Recently, on fighting a lot of Angels, I came upon the idea of a sacred unit killing weapon. We have several weapons that do X3 damage vs. undead, but none that do extra damage vs. sacred units.

Would it be unbalancing to introduce an artifact level weapon, that does X3 damage vs holy units? I'm not a modder, but it seems like it would not be hard to make one.