In reverse order:

• Directly mapping structs to JSON is a solved problem in userland for every major language
• yes it does, and worse it’s part of the return signature and null is super-prevalent of necessity as a result
• even java doesn’t do that any more, but fine I guess
• cool, but access modifiers actually make a lot of sense. Go’s solution to this is to use capitalisation as a marker, which has no ‘inferential readability’ – public/private is obvious. Foo/foo? Considerably less so

Further, meta programming in go sucks donkey balls. Sure, it finally got generics but also they suck. Last I checked it still didn’t even support covariance.