Pessimistic: CRISPR probably won't work well for IQ enhancement because the inheritable component of IQ is massively polygenic, likely encompassing tens of thousands of SNPs to predict only several percentage points of variability. only a few of those SNPs have enough individual impact to bother, worth a couple IQ points total. Selecting an initial batch of embryos based on single-cell sequencing and running the results through a GWAS model for IQ, then using those few specific high-value loci to set up parameters for either CRISPR or iterated embryo selection [1][2] could be a much more practical, if also much slower, approach.

Optimistic: IQ is massively polygenic as above but the relevant SNPs form clusters with directly traceable and quantifiable impact on the microstructure of the brain, responsible for much (up to 40 % and possibly more) of the observed inherited variability [3]. These clusters could be used to directly narrow down the target set for CRISPR.

[1] https://wiki.lesswrong.com/wiki/Iterated_embryo_selection
[2] http://onlinelibrary.wiley.com/wol1/doi/10.1111/1758-5899.12123/full
[3] http://www.cell.com/neuron/fulltext/S0896-6273(17)31092-9