I think releasing unique UR items would make the UR item problem worse, not better. The cakes are really for item collectors; there’s a bunch of other cake items that can do the job if you need a cake for a dressup. But if they were something unique, then there wouldn’t be anything to replace them if you wanted to make a dressup and that was the only item that fit. This would be especially a problem if the items were big; there are some very creative people who can make items for their dressup out of stuff like gingerbread house frosting, game pieces, paint splashes, etc. but those items are small, and even making a small accessory like a hat could take a hundred or more of them. I have tried to make a background out of paint splashes, for example, and despite the large numbers of paint items I have, it wasn’t enough to make anything with a significant amount of detail.
Plus, imagine the supply problem if it’s an item people want multiple of in a dressup!
I think if there were to be UR items, I would want them to be less “useful” and more “gimmicky”. Such as an item that “evolves” over time, like an item variation of the rotting fruits that were the original URs. Or, though I doubt how possible this would be, an item that changes every refresh, or one that cycles appearance based on the seasons or changes every couple days.