Well, I'd imagine "it slows to a crawl, they get tossed in a pile similar to items that were in a trade depot (assuming that's what happens to trade-depot-stored items, I don't visit abandoned forts much^^), depending on how adventure mode sites handle buildings (I tried advmode once, but it doesn't hold my interest. I'm a fortmode guy) there'd either still be a storehouse or see previous point, to combat this issue identical items could be numbered and I kinda doubt I'd realistically manage to create enough different roasts or whatnot to exceed DF's ability to count them (and if I could do that, I could just as easily - though slower due to low FPS - run into this without storehouses), I assume jobs would check "does the storehouse have <item>" so strange moods should be able to grab from them as well, mandates count whether you create the needed item on creation, so they could still count the item before it gets hauled to storage (how is this even an issue), and since the items are not lost why would the artist worry about them unless someone destroys the storehouse, at which point yeah, artist McThousandPiecesInThere will go mad.
what I want isn't neccesarily "the ability to design(ation) an exploitation zone(s)", what I WANT is to be able to play my fort and not worry that if my dwarves are TOO INDUSTRIOUS (seriously?) I will feel forced to start over because the game can't handle a thriving fort without some kind of supercomputer. If some other method allows this, nice. But with how long this has been a major issue (I think last time I didn't have to worry about producing too much the game was still in 2-D) I think it's time for some band-aid methods. I seriously care less about awesome new trees, a better job manager and friggin BARDS than about the ability to actually play a fort in a way that's fun, instead of a way that optimizes it for saving CPU cycles.