What kind of references do you want for a procedure that was just done for the first time? We already know that some diseases are affected by genes. It is also clear that intelligence is at least in part inheritable. It's a reasonable assumption that we can improve both if we get good at editing genes.
No, it is not. Heritability does not mean that there is a simple correlation between a trait and a small number of genes that could be exploited for targeted manipulation.
Take height: Height is extremely heritable. If your parents are both tall, you are very likely to be tall as well. But height is influenced by thousands of genes, and each individual gene has only a minuscule influence. And each of those genes is also responsible for many other unknown things.
It's not at all a reasonable assumption that genetic modification will allow us to influence a complex trait like intelligence. That's just wishful thinking.
On the other hand, we can (today!) predict height from raw sequence with correlation 0.65: http://www.genetics.org/content/210/2/477. It does not mean we can do such prediction for designed sequence (predictor likely will fail to generalize), but it can be used to select from natural variation. I don't see any wishful thinking here.
Yes, selecting the "tallest" embryo for implantation sounds somewhat feasible. It's similar to selective breeding with a shorter feedback loop. The only downside is that you are only selecting for genotype, instead of phenotype, so your model might accidentally select for some other things that you didn't expect.
But that's very different from designing an embryo by direct genetic modification.
Agreed, there's a big difference between what's possible with selection and what's possible with editing. Selection is already available (as increasingly sophisticated PGD). It's a lot trickier to do anything useful with editing.