The maintenance-cost framing is the useful constraint. I’d rather see agents default to smaller diffs, test scaffolding, and explicit assumptions than maximize lines changed per prompt.
I think this is still the role of human oversight, these tools will forever be imperfect and the instructions we give them as prompts will always been prone to inaccuracies/misinterpretation. I find it useful to evaluate the code and often ask for simpler solutions and so far it has produced slightly more elegant solutions. The tendency to spawn helper functions to solve every problem or doing things in a slightly weird or at least unconvential way when there is an easier/standard way of doing it that would create less code. Your ideas if automated would definitely make things more maintainable but even code produced my machines require a human to be responsible for making sure/verifying it works.