I will agree with bookwormde in that many factors will play into how any given child reacts to the experience at WDW, whether or not they have autism! Some parents are really surprised when their child reacts in ways that they could never predict. For our son who was 5 at the time, with autism, in some ways he reacted better to given situations than his two triplet sisters!! (ex not being scared of certain characters).
We knew going in that waiting situations such as waiting for fireworks and parades to start would be an issue for our son, so we brought along some amusements in his diaper bag, or somebody would take him for a walk while the others got our spot, or we would hold him, bounce him, do flips with him, etc. to give him the sensory feedback that he needed. In many ways he excelled while at WDW and that is why we are going back twice this year. He loved the rides, the fireworks, the characters, the dining experiences, just all of it! (He actually potty trained while there too which was fabulous!) In terms of
MNSSHP, he loved that too, the parade and fireworks, the trick or treating, etc. However, not knowing exactly how he would do, we kind of just had to take a chance and book it, and have some backup plans in place if you know what I mean.
I hope that helps -- feel free to PM me if you have any other questions that I can answer -- and I hope that you have a great trip!