Yes, I do see macros as a possible alternative to generics, but not sure if it would ever happen.

Macros are not an alternative to generics, they're an alternative to C++'s template specialisation.

Most languages with generics don't provide for user-controlled code generation via generics (if they do generics-based codegen at all, IIRC GHC uses erased generics for instance). They tend to use macro systems or preprocessors instead.

I know, but they surely would be a better solution than "go generate", as I doubt Go will ever have generics.