BERC-721
Declared behaviour for non-fungible tokens
The same question one layer over: a marketplace cannot tell whether a transfer will pay a royalty, whether an authority can revoke the token, or whether the metadata it rendered yesterday still describes the same thing. None of that is discoverable today, and the vocabulary BERC-20 uses does not transfer unchanged — a royalty is not a transfer fee, and per-token state has no analogue in a balance.
Nothing to read yet
There is no specification, no reference implementation and no test suite behind this entry — only the problem statement above. It is listed because stating the problem early is how the shape of it gets argued with, and because a work programme nobody can see is indistinguishable from one that does not exist.