Here is a good explanation provided by Ian Lance Taylor:
> This proposal is focused on code generation rather than language, and the details of how it changes the language are difficult to understand. Go is intended to be a simple language that it is easy to understand. Introducing complex semantics for performance reasons is not a direction that the language is going to take.
This was to allow for easy cross-compilation.
You should probably clarify that you are talking about 'golang plan9 assembly format', and not about the plan9 OS. This confused me a lot. (https://en.wikipedia.org/wiki/Plan_9_from_Bell_Labs)
I didn't know you could easily hand write 'golang assembly' for your functions. This seems really useful in some cases.
But I do wonder, why the std lib doesn't offer this ?
EDIT: I found the anwser: https://github.com/golang/go/issues/53171
Here is a good explanation provided by Ian Lance Taylor:
> This proposal is focused on code generation rather than language, and the details of how it changes the language are difficult to understand. Go is intended to be a simple language that it is easy to understand. Introducing complex semantics for performance reasons is not a direction that the language is going to take.