If humanity can make it another 100k years I think the spectrum and NT people will diverge to the point of being separate species, and if anything about hominid history tells me, one branch will club the other to death at some point.

I was thinking what a functioning society of people all possessing Down's Syndrome would look like if human history had taken a strange turn at the bottleneck, or the same circumstance for conditions like Tourette's.

Personally I think that neurodivergent people may be evolutionary solutions to very specific survival hurdles, and that we have not been facing these hurdles long enough for natural selection to smooth out the side effects. It's all very confusing at the individual level in a species specialization event as none of us will live long enough to see even the glimmerings of whatever shift in human existence that our daily struggles will initiate.