Comment by visarga

> If anyone knows of any work towards more open-ended fitness functions, I'd love to read it.

There is research in open-ended learning, see "Why Greatness Cannot Be Planned" by Kenneth O. Stanley. The core idea is that in open-ended scenarios you don't know what action was good except in hindsight because your path is deceptive. So the idea is to replace fitness with novelty search which provides more stepping stones towards the goal.