Which things do you have in mind?
> Why do you want structural typing there?
Isn't that a simplification? Instead of saying "here are types which you can use as e. g. parameter types, and here are types which you can't use (like in Java)", it says "all types work the same way".
I don't see the need of it if you already have a class-based system.
Go uses structural typing. But it is the only thing they have. Rust has traits, and it is the only thing they have.
I can't think now of more stuff but I remember you could even write xml in the language.
Like in Java?
new Object() { void foo() {}}.foo(); // Works
The point about XML is so stale already that I won't even bother commenting on it.
I care about simple, consistent rules. "X is a type, you can use it wherever you want" is one.
"X is a type, but there is also Y, which you can't really express in position A and B unlike X, but can only use it if you carefully avoid doing things #1 to #4" isn't one.
I don't think it helps for consistency when you have to ask yourself why some functionality is defined in terms of a trait if it could be defined in terms of the structural type and just providing the methods would be sufficient.