It's a gun that never entered the loot pool, much like the "Dubious Volley" late in Taken King & Rise of Iron. (eventually became The Wardcliff Coil in D2) Fate of all Fools was the same kind of gun in vanilla Destiny, and became The Jade Rabbit when Taken King came out. They have the same perks, however you'll notice that FoaF uses a pulse rifle model similar to The Stranger's Rifle instead of a scout model. It sucks that there's an unobtainable Grimiore card associated with it, but it's worth 0 points.