One problem is that for that approach, you would need, say, standardized IQ tests and genomes for a large number of people, and then to identify genome properties correlated with high IQ.

That's just a matter of time till genome sequencing get's cheap enough. There will be a day where it makes sense for China to sequence the DNA of every citizen for health purposes. China has also standardized test scores of it's population and no issues with racism that will prevent people from analysing the data.