In my personal project I've found having a hard lines of code limit has been a good limit on complexity. Makes me really ask if I need things.

One theory I have floating around in my head is that if a whole code base was microservices and micro front ends that were all less than 5,000 loc then you could fit the whole thing into a 100k token AI context window when working on it. And being few lines of code would force them to be somewhat simple

There is a limit, after a few 10,000's of LOC ai projects start disintegrating and becoming unmanageable.