All of the proposed explanations of the Flynn effect can be expressed in cultural evolution

Granted. I still don't think you could cause the Flynn effect by inducing cultural evolution (whatever that means). The reactionaries would have a field day regaling you with tales of Ethiopia and decolonization.

Modern cultural evolution is, on average, progressive. Fundamentally, that's because evolution is a giant optimization process operating in a relatively benign environment. The Flynn effect is one part of that.

It'd be the rent for believing cultural evolution is significantly relevant to the model.

Machine intelligence will be a product of human culture. The process of building machine intelligence is cultural evolution in action. In the future, we will make a society of machines that will share cultural information to recapitulate the evolution of human society. That's what memetic algorithms are all about.