[pjmlp]

Because they are a workaround for what should be a language feature in first place, just like on ML languages to type check structural types.

[flakes]

What exactly isn’t a language feature? Or do you have issues with semantics?

    var _ Foo = (*Bar)(nil)

The statement asserts that Bar struct pointers are assignable to a Foo interface.

I do agree it’s not as clean looking as the Java implements keyword, but it’s already a fairly terse pattern and IMO the inconvenience does not justify introducing new language syntax.