Hi! I have a lot of similarity with your training and background.
I have my PhD in school psychology, worked in public education for a few years, then transitioned to academic medicine. My time is currently split between a developmental center and a children's hospital.
At the children's hospital, I do pretty much what you would expect a pediatric neuropsychologist to do. My work at the developmental center, however, is different. Every neuropsychologist is first and foremost a psychologist, so conducting ASD evals is possible if you have the training. You may have to bill using different codes if the child does not have medical complexity that warrants neuropsychology codes. That's totally fine (in my state, psych eval and neuropsych eval codes are reimbursed at the same rate despite my grumblings).
You can have a blend of developmental and neuropsych easily. For example, children with spina bifida have complex medical histories and developmental concerns. Children with tuberous sclerosis have higher likelihood of autism than the general population. Neuropsychologists with neurodevelopmental training are perfect for children with genetic disorders and autism concerns, especially since several genetic conditions have epilepsy and/or brain tumors in the mix. In fact, I was telling a colleague today that we need to hire a neuropsychologist who specializes in neurodevelopmental disorders. While I have done it for years, it's not my clinical passion and the hospital leadership have plans for deployment in oncology clinics. I'm phasing out of a lot of the IDD/ASD cases (the "crawl under the table" testing), and we don't have anyone to fill that role once I transition to a different population.