How do we measure and compare prediction quality in a symbolic/deterministic context that also punish for complexity? I struggled on this in my phd thesis and had to brew my own Minimum Description Length implementation because I found nothing applicable. The statisticians I interrogated were like "don't try to do model selection on symbolic models, make them probabilistic and work from there"

The approach here assigns a cost to each operator, variable and constant. See docs.

Are you familiar with NSGA-2? That was the one I used in my PhD work.

A lot of research in GP/SR went toward methods for balancing density and selection from the pareto front.

One of the bigger problems is growth of meaningless equation material to counteract other pressures in the algorithm, which itself leads to premature convergence on suboptimal solutions. I had some thoughts at the time about ways to penalize this during the growth phase in my own algo, but never got around to them. Mainly needs bookkeeping for contribution to the final equation output.