I'm not sure though but I think I read that CryptoKitties (unique, non-fungible tokens) was only possible because of ERC223 and that it's a new feature of it. When I read about SMT's I realized they were more like ERC20 than ERC223 tokens. So creating types of items is possible through that, but creating a single, unique item it's not really usuable for it.

Since you mentioned CryptoKitties in the above post I thought perhaps BTS was ahead of Steem with UIA/SMTs, so maybe unique tokens are possible throug UIA's?
Anyway, I'm not well versed enough in this stuff to really know what i am talking about. But if you guys get together and figure it out, all the better!