PEP 544 supports structural typing, but to declare a structural type you must inherit from Protocol.
That smells a lot like nominal typing to me.

I'm not sure what inheriting from Protocol has to do with nominal typing, even though I would personally prefer to have a separate keyword for declaring protocols. But current typing philosophy is to prefer structural over nominal typing:

• Use abstract types like "Iterable" or "Sequence" over concrete types list "list".
• Use protocols instead of instances where it makes sense (although pragmatism very often means using an existing concrete class instead of defining a protocol).
• We are slowly replacing typing.IO et al. with more restricted protocols.

Personally I think that the typing infrastructure should move even more towards structural typing than it does at the moment and there is certainly a lot of room to grow. But overall I feel that typing is moving towards allowing more duck typing than it does at the moment.

 - Sebastian