I think it may be unclear that net worth and high education are a 1:1 proxy for IQ as many of the highest educated and highest earning individuals may be in that situation not because of raw IQ, but due to the other socioeconomic factors which lead to those conditions. Namely being born into high net worth households and being afforded extensive tutoring and supplemental education relative to their poorer peers. I accept the premise that highly educated households do correlate with high net worth, and the study's TFR findings relative to those points are interesting.

However, there is still a nonlinear relationship between high IQ and those factors, as well as between high IQ parents' offspring IQ levels. Not a few high net worth individuals choose mates based on factors distinct from having a similar or even a high IQ, if a strong correlation between genetic heritability and IQ is to be believed.

The study actually tracked high income with regards to increased TFR in the US and UK, while the correlation to high education was primarily in Sweden. This serves to weaken the connection between IQ and fertility as there are numerous high income situations which are specifically not correlated with high IQ or high education.

So, yes, having children is increasingly expensive especially in America, and wealthier people are more prolific. This does not appear, at least to my mind, to have direct bearing on observable trends in general population IQ in the short term, nor does it appear to be addressing future outcomes regarding the Idiocratic potential.