>>8
Autism is a lot like homosexuality in one important respect, which guarantees that even when a race is old and dying and produces unhealthy numbers of deviants, they would never be able to supersede the mainline.
Also autists need neurotypicals to build basements for them, supply said basements with electricity, computer parts, and food, and so on. So even if autists were able to reproduce, they would enter into a host-parasite relationship with neurotypicals, which obviously can't end with parasites "superseding" the host.