autism researcher here. I have not yet read this study. It will not be the kind of paper that many, including myself, can read quickly and understand. Autism is a multi-disciplined science, so there is a lot to understand. However, my initial sense from reading the abstract is that this paper might be a really really big deal and incredible new resource.

General problem statement: Many different genes variants are associated with autism, some strongly, most very weakly. Many have suspected that this plethora of genetic variants might converge onto a smaller set of biological pathways affecting neurodevelopment in ways that results in an autism phenotype or phenotypes. This has been our hope, because the alternative scares the hell out of a scientist. The saying goes that if you met one person with autism, you've met one person with autism...meaning there is a ton of heterogeneity within the autism spectrum, even if a certain set of core autism symptoms are displayed. So there was a existential crisis that there is no "autism", just a billion autisms, where your sample size is always N=1. By demonstrating evidence that many variants converge on the same biological pathways, there is hope that understanding autism is tractable.