My (admittedly limited) understanding is that each detectable genetic feature has a whole panoply of effects, some of which wont' be apparent at birth. Selecting for intelligence through specific genes is like to also be selecting for weak bones, reduced longevity, or other unpredictable side-effects.

Maybe one day it will be possible but there's a chasm between here and there which can only be crossed by extensive testing on real people. Is that even crossable?