This is basically polymorphization, mentioned in the blog post. The prototype implementation is in progress.
> The axiom is “monomorphic data, polymorphic code”. In other words, unlike languages like Haskell and OCaml that generally rely on uniform representations (boxing) to enable polymorphic code generation, data layouts will stay the same under polymorphization, and only function ABIs will change. [...] Go’s gcshape is somewhat analogous to our concept of data layouts.