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IQ is largely irrelevant to economic productivity and almost COMPLETELY irrelevant to social power; just look who we have in the White House if you're tempted to disagree (or who we MIGHT HAVE HAD, if you still do). Take a black child out of poverty and stick them in a wealthy Western household with a proper education and a diet composed of more than literal garbage, and they will grow up to be a productive adult.
That said, an IQ test measures little more than your proficiency at taking IQ tests. It was NEVER a measure of intelligence; it was a measure of educational achievement as a tool to focus on struggling schoolchildren with poor learning ability, and at best has a tenuous connection with adult intelligence except in extreme cases (like profound retardation: <20IQ). Studies have shown that people with higher IQs don't achieve more as adults but for statistically insignificant amounts.
So you could do this, sure, but nothing would change. The only thing that will is waiting for most of them to die, and then raising the living conditions up to a Western standard for the survivors. Doing it BEFORE letting them die is more humane, sure, but will probably collapse the global economy by the end of the century, likely leading to widespread war and the end of civilization. There's just too fucking many of them.