If the hypothetical high level language doesn't allow for ambiguous meanings, you can write a compiler for it and you don't need the AI.
(Not saying you're wrong about "higher and higher levels of abstraction" - that's the way it's always been - but the unique promise of AI is the ability to deal with ambiguity in the requirements).
Assuming a (hypothetical, doubtful) AI as good as a human programmer, I think the advantage becomes speed. Think of it like a REPL that you program in English. Patching ambiguities with "Oh, I didn't mean X, I meant Y" becomes the work of minutes, not hours.
In this case, you don’t really need AI. People like Forth and Lisp because you can built an efficient DSL which you can converse with. What people have trouble with is formalism, and logical and abstract reasoning.
(Not saying you're wrong about "higher and higher levels of abstraction" - that's the way it's always been - but the unique promise of AI is the ability to deal with ambiguity in the requirements).