The thing to note is that the worldview of social justice advocates is not "advocate for all oppressed groups", it's "advocate for all oppressed groups
up to intersectionality". At least in America, we used to go through phases of, say, black power groups being kinda sexist, and women's liberation movements being hella racist. This poses a unique opportunity for people who oppose both: just use one to harm the other. For example, the founder of Planned Parenthood was willing to advocate for themselves in the language of eugenics, so if you hate abortion rights, you just constantly bring up all the awful things they said about black people. There's nothing stopping you from switching tactics a day later and complaining about, say, a BLM riot that winds up shutting down a Planned Parenthood clinic.
The social justice advocate's response to that is intersectionality: a defense mechanism of not engaging in advocacy that would benefit one oppressed group at the expense of another. They're not always great at this - some social conflicts are just difficult to actually make judgments on (e.g. Israel/Palestine). The thing is, though - I doubt "drop the autistics" is going to pick up steam in social justice circles. Autism, and neurodivergence in general, tracks very well with queer sexual orientations and gender identities. Social mores intended to enforce rigid gender roles and heteronormativity simply don't work on people who can't parse them. (The contrapositive of this is why there's a huge push for non-gendered children's toys.) Ergo, it's very unlikely that you'd see the social justice left tear itself apart like this, and more likely that you'd see people arguing that "drop the autistics" is bullshit.
I'm also going to point out that, as an autistic person myself, the stricter speech rules of the social justice left aren't terribly difficult to parse. The prior eras of social mores were far stricter because we didn't see them as coercive and thus didn't question their power, and it's somewhat troubling that people don't view it as an improvement from what we had before. It's sort of like how people coming from proprietary software sometimes argue that the GPL is non-free because it has some restrictions that don't conform to the unstated mores of proprietary licensing. Much of the reaction people have to these speech rules comes from two different places:
1. The people reacting to these rules are neurotypical, and used to invisible speech rules enforced by people with a common cultural heritage such that they wouldn't disagree on their unstated rules.
2. Many people in the social justice community are autistic (see above) and also had a hand in writing the rules. Of course, if people who can't parse social cues write the rules of a society, those rules are going to be explicitly stated rather than inferred.
In other words, the problem isn't that the social justice left is going to throw out neurodivergent people, it's that the social justice left is autistic, in cultural control, and writing the new rules of society in a way neurotypicals don't understand.
(Side note: #9 is a conflict that's been brewing in the back of my head for a while now. I love P2P tech but think the entirety of cryptocurrency has been a dead-end full of scams.)