>codebases for production code will be so low in quality that they will be unintelligible to humans, and LLMs, too, will have trouble maintaining them

The concern for code quality has become increasingly unfounded. I have noticed over the last year or so that you can still tell when a codebase is 100% AI generated, but not because it is poorly written or disorganized, but that it is now dramatically better than any human would have written.