Not a bad idea. All of the mechanics are in place, minus the surgery skill (I'd use a roll from existing skills, no need to add a third set of misc ones yet at least). I want to reduce both the effectiveness and number of severed limbs you come across. Losing, say, an arm might cost you 3 strength, and attaching it only regains 2.
Maybe I'll come back to this once I implement diseases such as leprosy and such. Swapping out limbs might have a much more of an advantage then. Right now it wouldn't do much but hurt your character.