Although this question was asked many years ago, I am ready to have that set. I know it has been mentioned elsewhere how there is already a Psychology and Neuroscience Stack Exchange, but from the description (and a quick view of the most recent questions) I personally see it as the people who are studying or have studied these topics being the ones answering these questions. Of course, each doctor, nurse practitioner, and people studying science have a great amount of research or current studies to be able to answer questions that have occurred or are occurring, but psychology especially is difficult to receive every detail because not everyone there is the one experiencing the life of the person they help.
While they can definitely have results on heart rate, it's uncertain they are the ones experiencing those conditions being brought up. However, the people who can answer questions such as "At what point should I bring to the school that their existing accessibility support is in need of more staff, focus, money, support, utilities, etc.?": Therapists and psychiatrists would likely say "You can do it now", but others that have already personally experienced a similar feeling may understand a little more on why they are asking a community such as this new one being suggested rather than the school or the Psychology Stack Exchange.
I understand, my point of view on which direction this possible, new Stack Exchange will be towards is probably a little different from yours, but I think having it be towards those diagnosed with such disabilities or personally experiencing similar things is a wonderful idea. For your example question of "Can you explain to me how I can do... [something linked to PC]?" can now even be answered by Alexa, but would Alexa have the personal user experience of not knowing how this PC thing works while having a limited vision? A person who is also blind would take into consideration "this part can be easy to find, but maybe not this part unless with this screen reader because that other screen reader did not work well for me due to this reason".