He mentions that a: autists are dumber (i.e. do not express some or most of the markers for high intelligence) but posess the genetic markers, and b: the expression of intelligence markers of siblings/parents/higher-order relatives of autists (specifically) is understudied and recommends it for further study. [As far as I read it anyway]

I do believe that the "imbalance"-hypothesis he presents is a bit vague and proposes several imbalances according to different (and possibly orthogonal) models for intelligence, making it seem a bit unfalsifiable to me. Who knows. Behavioral neuroscience based on MRI(or similar modalities) is a giant sandcastle anyway, best not stack those results too high.