Maybe if it was like the Glass Swords from Ultima (kills anything in one hit, then immediately breaks), that'd be cool. Of course, they'd have to change the durability to 1. You can get a lot of use out of this. Just put it on a dual-wielding warrior, Rage, Crippling Blow, then change out that weapon. Considering the damage you'd get out of it, it'd be worth the extra AP cost of changing weapons. Wouldn't even need Rage, really, as a non-critical Crippling Blow with that equipped would kill absolutely anything in one hit outside of the final battle.
So, as is, in the words of Fluffington: Terrible idea.
