Ironically, college admissions would get a lot more egalitarian if they switched to IQ tests, because the long list of confounding factors (or "privileges" as some people call them) like the availability of free hours to study in, have much less impact on matching abstract symbols in rows than they have on the SAT or other partially knowledge-based tests.

I'm not sure if we want to do that because the capacity for working hard is often more valuable than "g". One's capacity and willingness to work hard for a long time is impossible to untangle from one's circumstances including one's upbringing. Fairly testing for that is much harder than testing for g but it may be too crucial to ignore.

It probably wouldn't make much difference. There's pretty good correlation between SAT and IQ. See e.g. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6963451/

That correlation is not invariant to cultural factors. Your own link mentions some of these - namely, "epistemic belief of learning, performance-avoidance goals, and parental education", for which we can easily measure variation across ethnicity (which of course is a lot more visible and more easily operationalized that a more nuanced understanding of culture, including urban vs. rural).

The paper you linked doesn't report the correlation as far as I could see, but it did cite a paper that said it was 0.86[0]. That's great for a social sciences correlation, but not so great as a way to be fair. 0.86 leaves a lot of room for other processes - and in competitive scenarios at the top of the distribution, the confounders could make all the difference.

[0] https://pubmed.ncbi.nlm.nih.gov/15147489/