I consider checked exceptions in Java quite a nightmare. You have to specify the classes of exception you might throw as part of your function signature and in all methods which might propagate. This is quite a buerocratic monster, which requires quite a bit of refactoring if your exception signature changes. Alternatively, all methods in the chain tend to catch all and then rethrow others.

The described changes could have been added by anyone in earlier Go versions. These are not things which can be only implemented by the language or compiler implementor, these are just APIs, which are standardized.