The standard for humans is a clean room reimplementation so I guess you'd need 2 AIs, one to translate A into a list of requirements and one to translate that list back into code.

But honestly by the time AI is proficiently writing large quantities of code reliably and without human intervention it's unclear how much significance human labor in general will have. Software licensing is the least of our concerns.

If that's legal then copyright is meaningless which was the original intention of the GPL.

So, uncopyrightable AI generated code is actually a good thing from open source community standpoint?

Presumably depends on the impacts. It's an ideology that seeks user freedom. If you need access to the source code to use as a template that clearly favors proprietary offerings. But if you can easily clone proprietary programs that would favor the end user.

How would this kind of mechanical translation fail to be a violation of copyright?