I predict there's always going to be a Wirth's law or Peter principle of slopcoding — it will always be easier to tack on a new feature than to understand a whole system and clean it up.

Alternatively stated: codebases will expand to the limit of an organization's ability to manage them, so the equilibrium will remain at the point of near, but not total, incomprehensibility.

It's not true, a newer model can do better to clean things up but you can't brute force engineer your way out of a shit design.

It's definitely true. I didn't use AI at all until this January because the code it wrote was too bad. Now I'm comfortably using AI for less important programming tasks and it's okay as long as you steer it carefully. I see no reason why it wouldn't get better up to a point that AI written code is better than what any human programmer could produce. It's also constantly getting better at refactoring.