I think it's a good idea, if only for its implications. To cater to 200 dwarves and nobles (who would of course require their own private toiletries), vast sewer systems would need to be constructed beneath the fortress (which is possible now with z-levels). These sewers would come to be infested with all manner of loathsome creatures, trolls, maybe otyughs and whatnot. Goblin thieves could use them as a convenient point of entrance. Entire raiding could sneak through them. Perhaps, though, the dwarves would construct complicated systems of levies and floodgates and, when a raid was approaching, pull the lever and drown them in sewage.
Chasming sewage could lead to attacks by chasm-dwellers, sneaking up through the sewer systems to emerge from the communal bathrooms beneath the great hall. Attacks out of toilets would give Urist McNoble a good reason to always have a couple of personal guards present, in case he finds himself under attack in his own quarters. In adventure mode, sneaking through sewers is practically an archetypal activity.
And, if Toady ever decides to add diseases, sewage would suddenly become even more important. Appropriate waste-disposal systems would be a necessity
Poop for its own sake would be fairly worthless (I don't want bricks made out of it or anything), but, as a whole, I think sewage disposal would add another v interesting layer of complexity to the game.