This is a question I've been wondering for a while, but no matter how much I search, I just can't find any relevant results. I'm hoping that the people of this community can provide some resources about this topic, or if nothing else some interesting conjecture or discussion.
The sort of specific inspiration behind this question was thinking about how autistic people are a source of very innovative language use, and are often more likely to acquire and never unlearn "wrong" forms of words or grammar. A handful of linguistic traits that I've seen pathologized in autistic people where I live are more or less accepted in the speech of some other speech communities around the world. So, given some people's beliefs on the role of autistic people in prehistory, could a historical speech community looking to adopt distinctive speech patterns, turn to its neurodiverse population for inspiration?
But I'm also curious about disabilities or disorders aside from autism. How have things like deafness/hearing impairment, blindness/visual impairment, facial paralysis or motor issues, dyslexia, intellectual disability, limb loss, and so forth, affected spoken language, written language, and signed language, as used by language communities as a whole? With regard to sign language, I've heard that the high rate of blindness among the Deaf community of Honduras' Bay Islands resulted in the development of a tactile form of the local village sign. I'm sure that given the rate of disability prior to modern medicine, probably especially among venerated elders, that some amount of language development in the world must have been motivated by accessibility in the same way as BISL — or at the very least caused by inaccessibility, i.e. mishearings or mispronunciations due to disability getting passed on to abled acquaintances.
So yeah. Even though most of the world has for a pretty long time now been pretty ableist, and this is reflected in many languages' vocabularies, I'm still wondering if there are any linguistic clues that our abled ancestors did in fact try to take good care of their disabled brethren. This is what the archaeological record seems to show, so how about the linguistic record?
I have noticed this too, but it is something that's highly variable, like with anything on a spectrum. My brother and I are both autistic, but he struggles a lot more with conversational maxims than I do. It's to the point where half of his utterances are perfectly grammatical but also completely meaningless for anyone else, because his way of processing and using language just isn't supposed to be cooperative. I've heard people say that conversational maxims are socially determined, so for someone who generally doesn't follow social norms, it makes sense to understand and use language with different conversational maxims as well.
In some ways, my brother's way of speaking is comparable to Darmok from Star Trek, because it often relies primarily on a very rich set of allegories based on his interests, that he's the only person who actually knows how to decode. I swear that I read or heard somewhere about what this type of autistic speech is actually called, but I don't remember.
Anyways, there are some people who believe that without the social pressures of masking, that there would've been a lot more people who we'd now call neurodiverse, and that these would've also been more integrated into broader society, with specific roles best suited for their neurotypes. So if that were true, then I could see this group being "patient zero" for the spread of some sort of unconscious language change, and maybe even having some sort of prestige. Who knows, though.
Edit: Because I feel like this idea of "ancient autism" is sort of modern mythology, even though I want to believe it and don't think it's necessarily false.