I think it'd be a pretty sweet to have recipes drop from dungeons. It'd be good incentive for us crafters to run older dungeons again just to get that recipe. Maybe even make it so the recipe drop is for rare weapons and armor, like the Foestriker's Set, or the Battlemage's set. Sometimes the boss won't drop the equipment, but instead the recipe for a piece of it.

Of course, for balance purposes, make it incredibly hard to make (ie, 500 of whatever shards your class uses, materials 10 levels above what you have, lower durability, incredibly high difficulty, etc.)