I agree 1000% that the full spectrum of autism must be included into autism research.
My research for the last 10 years has been dedicated to collecting and analyzing data for the Autism Phenome Project [1]. Unlike almost all autism neuroimaging research, we include the full spectrum of autism, with a third of our participants with severe intellectual disabilities, closely matching their share of the autistic population, as well as those who are non-verbal, have extreme specific phobias and anxiety, sensory sensitivities, self-injurious behaviors: the full spectrum. It still frustrates me to no end that almost every neuroimaging study you read by default excludes those with IQs less than 80, while our cohort has managed, through very hard work, managed to image individuals with IQs in the 20-60 range with regular success.